:"  5  *  K  E  L  E  Y 
SARY 
JNIVERSITY  OF 
CALIFORNIA 

EARTH 

SCIENCES 
LiC.v 


DANA'S  MANUAL 
OF  MINEBALOGY 


FOR  THE  STUDENT  OF  ELEMENTARY  MINER- 
ALOGY, THE  MINING  ENGINEER,  THE 
GEOLOGIST,  THE  PROSPECTOR, 
THE  COLLECTOR,  ETC. 


BY 

WILLIAM  E.   FORD 

Assistant  Professor  of  Mineralogy  in  the  Sheffield  Scientific 
School  of  Yale  University 


THIRTEENTH  EDITION 

ENTIRELY   REVISED   AND   REWRITTEN 
TOTAL  ISSUE,   THIRTY-FIVE  THOUSAND 


NEW  YORK 
JOHN  WILEY  &  SONS,  INC. 

LONDON:  CHAPMAN  &  HALL,  LIMITED 


EARTH 

SCIENCES 

LIBRARY 


GOPTBIGHT,  1912, 
BY 

S.  DANA.  AKD:  WILLIAM  E.  FORD 


,  19t2,(£K  GBEfAT  BRITAIN 


Stanbopc  ipreas 

H.  GILSON   COMPANY 
BOSTON.  U.S.A. 


EARTH 

PREFACE.  SCIENCES 

LIBRARY 

THE  "  Manual  of  Mineralogy  "  was  first  published  by  James 
D wight  Dana  in  1848.  A  second  edition  was  printed  in  1850 
and  a  "New  Edition,"  which  had  been  revised  and  enlarged, 
was  published  in  1857.  The  book  was  rearranged  and  rewritten 
for  the  third  edition  which  appeared  in  1878.  This  edition 
included  an  extensive  chapter  on  rocks,  and  the  title  of  the  book 
was  changed  to  "Manual  of  Mineralogy  and  Petrography."  The 
fourth  and  last  revision  was  published  in  1887.  Since  that  time 
the  book  has  been  frequently  reprinted,  so  that  the  last  edition 
was  the  twelfth.  But  it  is  now  twenty-five  years  since  the  last 
revision  of  the  text.  Believing  that  the  Manual  has  amply 
proved  its  usefulness,  and  with  the  desire  of  keeping  the  series 
of  the  Dana  Mineralogies  complete,  Professor  Edward  S.  Dana 
asked  the  author  to  prepare  a  new  and  revised  edition. 

It  was  found  that  it  was  desirable  to  rewrite  the  book,  and 
consequently,  as  far  as  the  text  and  figures  are  concerned,  this 
present  edition  is  almost  wholly  new.  The  scope  and  character 
of  the  book,  however,  have  been  kept  as  nearly  as  possible  the 
same.  The  book  has  been  primarily  designed  to  fill  the  ordinary 
needs  of  the  elementary  student  of  Mineralogy,  the  mining 
engineer,  the  geologist  and  the  practical  man  who  may  be 
interested  in  the  subject.  It  has  been  made  brief  and  direct 
and  the  treatment  has  been  as  untechnical  as  possible. 

The  chapter  on  Petrography  has  been  omitted  and  only  a 
brief  and  general  description  of  the  various  important  rock  types 
given.  This  change  was  made  in  view  of  the  fact  that  since 
1887  the  subject  of  Petrography  has  had  so  large  a  development 
as  to  render  impossible  its  adequate  treatment  in  a  single 
chapter.  Moreover,  several  elementary  books  on  the  subject, 

iii 


469983 


IV  PREFACE 

notably  "Rocks  and  Rock  Minerals"  by  L.  V.  Pirsson,  are  now 
available.  Because  of  this,  the  title  has  been  changed  again  to 
its  original  form  and  the  book  is  to  be  known  in  the  future  as 
"  Dana's  Manual  of  Mineralogy." 

The  order  adopted  in  the  description  of  species  has  been 
changed  to  that  of  the  chemical  classification  as  used  in  the 
System  of  Mineralogy.  It  was  felt  that  this  was,  on  the  whole, 
the  most  logical  and  useful  arrangement.  Following  the  de- 
scription of  the  individual  species,  however,  various  tables  are 
given,  among  them  one  in  which  the  minerals  are  grouped 
according  to  their  chief  element.  After  each  such  list  a  general 
description  of  the  association  and  occurrence  of  the  minerals 
which  it  contains  is  given.  Statistics  of  mineral  production, 
etc.,  are  given  in  Appendix  II.  It  is  intended  by  frequent 
revision  of  this  portion  of  the  book  to  keep  the  figures  reasonably 
up  to  date. 

The  author  has  made  free  use  of  many  sources  in  the  prepara- 
tion of  the  book.  He  is  especially  indebted  to  the  sixth  edition 
of  "Dana's  System  of  Mineralogy"  and  the  "Text  Book  of 
Mineralogy"  by  E.  S.  Dana,  to  the  " Brush-Penfield  Deter- 
minative Mineralogy  and  Blowpipe  Analysis  "  and  to  "  Rocks 
and  Rock  Minerals"  by  L.  V.  Pirsson.  He  acknowledges 
gratefully  the  constant  advice  and  criticism  of  Professor  Edward 
S.  Dana. 

SHEFFIELD  SCIENTIFIC  SCHOOL  OF  YALE  UNIVERSITY, 
NEW  HAVEN,  CONN.,  June,  1912. 


INTRODUCTION. 


MINERALS  are  the  materials  of  which  the  earth's  crust  consists 
and  are  therefore  among  the  most  common  objects  of  daily  obser- 
vation. A  mineral  may  be  defined  as  a  naturally  occurring  sub- 
stance having  a  definite  and  uniform  chemical  composition  with 
corresponding  characteristic  physical  properties.  This  elimi- 
nates all  artificial  products  of  the  laboratory  which  may  conform 
to  the  last  part  of  the  definition.  It  also  eliminates  all  natural 
products  of  organic  agencies,  since  they  will  not  show  the  uni- 
form chemical  and  physical  characters  demanded  of  a  mineral. 

In  the  form  of  rocks,  minerals  make  up  the  solid  matter  of  the 
earth's  crust.  But  in  the  great  majority  of  cases  a  rock  is  not 
made  up  of  a  single  mineral,  but  is  a  more  or  less  heterogeneous 
aggregate  of  several  different  species.  A  few  rocks,  like  lime- 
stone and  quart  zite,  consist  of  but  one  mineral  in  a  more  or  less 
pure  state.  In  addition  to  occurring  as  essential  and  integral 
parts  of  rocks,  minerals  are  found  distributed  through  them  in 
a  scattered  way,  or  in  veins  and  cavities.  Water  is  a  mineral, 
but  generally  in  an  impure  state  from  the  presence  of  other 
minerals  in  solution.  The  atmosphere  and  all  gaseous  materials 
set  free  in  volcanic  and  other  regions  are  mineral  in  nature. 

Characters  of  Minerals. 

1.  Minerals,  as  previously  stated,  have  a  definite  chemi- 
cal composition.  This  composition,  as  determined  by  chemical 
analysis,  serves  to  define  and  distinguish  the  species,  and  indi- 
cates their  profoundest  relations.  Owing  to  difference  in  com- 
position, minerals  exhibit  great  differences  when  subjected  to  the 
action  of  various  chemical  reagents,  and  these  peculiarities  are 
a  means  of  determining  the  kind  of  mineral  under  examination 


VI  INTRODUCTION 

in  any  case.  The  department  of  the  science  treating  of  the  com- 
position of  minerals  and  their  chemical  reactions  is  termed  Chem- 
ical Mineralogy. 

2.  Each  mineral,  with  few  exceptions,  has  its  definite  form, 
by  which,  when  in  good  specimens,  it  may  be  known.     These 
forms  are  cubes,  prisms,   pyramids,   etc.      They  are  included 
under  plane  surfaces  arranged  in  symmetrical  order,  according 
to  mathematical  law.     These  forms  are  called  crystals.     Besides 
these  outward  forms  there  is  also  a  distinctive  internal  structure 
for  each  species.     The  facts  of  this  branch  of  the  science  come 
under  the  head  of  Crystallographic  Mineralogy. 

3.  Minerals  differ  in  hardness,  from  talc  at  one  end  of  the 
scale  to  the  diamond  at  the  other.     Minerals  differ  in  specific 
gravity,  and  this  character,  like  hardness,  is  a  most  important 
means  of  distinguishing  species.     Minerals  differ  in  color,  trans- 
parency, luster  and  other  optical  properties.     The  facts  and 
principles  relating  to  the  above  characters  and  others  of  a  similar 
nature  are  included  in  the  department  of  Physical  Mineralogy. 

4.  The  detailed  descriptions  of  individual  mineral  species, 
including  their  chemical,  crystallographic  and  general  physical 
characters,  together  with  their  occurrence,  associations,  uses,  etc., 
are  included  under  the  division  known  as  Descriptive  Mineralogy. 

5.  Lastly,  the  discussion  of  the  methods  that  are  used  for 
identifying  minerals  forms  the  division  known  as  Determinative 
Mineralogy. 

These  different  branches  of  the  subject  are  taken  up  in  this 
book  in  the  following  order:  I.  Crystallographic  Mineralogy; 
II.  Physical  Mineralogy;  III.  Chemical  Mineralogy;  IV. 
Descriptive  Mineralogy;  V.  Determinative  Mineralogy. 


TABLE   OF  CONTENTS. 

PAGE 

INTRODUCTION v 

I.  CRYSTALLOGRAPHY. 

INTRODUCTION 1 

SYMMETRY 7 

CRYSTAL  NOTATION , 9 

DEFINITION  OF  VARIOUS  TERMS 12 

ISOMETRIC  SYSTEM 16 

TETRAGONAL  SYSTEM 31 

HEXAGONAL  SYSTEM 37 

ORTHORHOMBIC  SYSTEM 47 

MONOCLINIC  SYSTEM 50 

TRICLINIC  SYSTEM 54 

H.  GENERAL  PHYSICAL  PROPERTIES  OF  MINERALS. 

STRUCTURE  OF  MINERALS 57 

CLEAVAGE,  PARTING  AND  FRACTURE 59 

HARDNESS  OF  MINERALS  . 60 

TENACITY  OF  MINERALS 62 

SPECIFIC  GRAVITY  OF  MINERALS 62 

PROPERTIES  DEPENDING  UPON  LIGHT 

Luster 65 

Color  of  Minerals 67 

Refraction  of  Light  in  Minerals 68 

Double  Refraction  in  Minerals 71 

PYROELECTRICITY 72 

III.  CHEMICAL  MINERALOGY. 

CHEMICAL  GROUPS 74 

DERIVATION  OF  A  CHEMICAL  FORMULA 75 

CALCULATION  OF  PERCENTAGE  COMPOSITION 76 

ISOMORPHISM 77 

ISOMORPHOUS  GROUPS 79 

DIMORPHISM,  TRIMORPHISM,  ETC 80 

INSTRUMENTS,  REAGENTS  AND  METHODS  OF  TESTING 80 

TESTS  FOR  THE  ELEMENTS 93 

vii 


Vlll  CONTENTS 

FACM 

IV.  DESCRIPTIVE  MINERALOGY. 

DESCRIPTION  OF  SPECIES 115 

LISTS  OF  MINERALS  ARRANGED  ACCORDING  TO  ELEMENTS.  .  309 
OCCURRENCE  AND  ASSOCIATION  OF  MINERALS 

Rocks  and  Rock-making  Minerals 328 

Pegmatite  Dikes  and  Veins 345 

Contact  Metamorphic  Minerals 347 

Veins  and  Vein  Minerals ' 349 

LISTS  OF  MINERALS  ARRANGED  ACCORDING  TO  SYSTEMS  OF 

CRYSTALLIZATION 354 

V.  DETERMINATIVE    MINERALOGY. 

INTRODUCTION 364 

DETERMINATIVE  TABLES 369 

INDEX  TO  DETERMINATIVE  TABLES 434 

APPENDIX  I.     LIST  OF  MINERALS  FOR  A  COLLECTION 436 

APPENDIX  II.     MINERAL  STATISTICS 437 

INDEX 451 


MANUAL  OF  MINERALOGY. 


I.   CRYSTALLOGRAPHY. 
I.   INTRODUCTION. 

THE  great  majority  of  our  minerals,  when  the  conditions  of 
formation  are  favorable,  occur  in  definite  and  characteristic 
geometrical  forms  which  are  known  as  crystals.  To  gain  a  com- 
prehensive knowledge  of  the  laws  which  govern  the  shape  and 
character  of  crystals  is  a  very  important  part  of  the  study  of 
mineralogy.  This  division  of  the  subject  is  called  crystallog- 
raphy. It  forms  almost  a  separate  science  in  itself,  and  to  ade- 
quately and  exhaustively  discuss  it  would  require  a  volume 
much  larger  than  the  present  one.  In  the  following  section, 
however,  the  attempt  will  be  made  to  present  the  elements  of 
crystallography  in  a  brief  and  simple  manner  and  at  least  to 
introduce  the  reader  to  the  more  essential  facts  and  principles 
of  the  subject. 

A  crystal  has  been  defined  as  follows:  A  crystal  is  a  body  which 
by  the  operation  of  molecular  affinity  has  assumed  a  definite  internal 
structure  with  the  form  of  a  regular  solid  inclosed  by  a  certain  num- 
ber of  plane  surfaces  arranged  according  to  the  laws  of  symmetry* 
This  is  a  very  compact  definition  and  several  pages  will  be  devoted 
to  its  discussion. 

A  better  idea  of  the  fundamental  laws  of  crystallography  will 
be  obtained  by  first  considering  the  three  prominent  modes  of 
crystallization.  Crystals  are  formed  by  crystallization  either 
(1)  from  a  solution,  (2)  from  fusion,  or  (3)  from  a  vapor.  The 
first  case,  that  of  crystallization  from  solution,  is  the  most  familiar 
to  our  ordinary  experience.  Take  for  example  a  water  solution 

*  Century  Dictionary. 

1 


OF -MINERALOGY 

containing  sodium  chloride  (common  salt).  Suppose  that  by 
evaporation  the  water  is  slowly  driven  off.  The  solution  will, 
under  these  conditions,  gradually  contain  more  and  more  salt 
per  unit  volume,  and  ultimately  the  point  will  be  reached  where 
the  amount  of  water  present  can  no  longer  hold  all  of  the  salt 
in  solution,  and  this  must  begin  to  precipitate  out.  In  other 
words,  part  of  the  sodium  chloride,  which  has  up  to  this  point 
been  held  in  a  state  of  solution  by  the  water,  now  assumes  a  solid 
form.  If  the  conditions  are  so  arranged  that  the  evaporation  of 
the  water  goes  on  very  slowly,  the  separation  of  the  salt  in  solid 
form  will  progress  equally  slowly  and  definite  crystals  will  result. 
The  particles  of  sodium  chloride  as  they  separate  from  the  solu- 
tion will  by  the  laws  of  molecular  attraction  group  themselves 
together  and  gradually  build  up  a  definitely  shaped  solid  which 
we  call  a  crystal.  Crystals  can  also  be  formed  from  solution  by 
lowering  the  temperature  or  pressure  of  the  solution.  Hot 
water  will  dissolve  much  more  salt,  for  instance,  than  cold,  and 
if  a  hot  solution  is  allowed  to  cool,  a  point  will  be  reached  where 
the  solution  becomes  supersaturated  for  its  temperature  and 
salt  will  crystallize  out.  Again,  the  higher  the  pressure  to  which 
water  is  subjected  the  more  salt  it  can  hold  in  solution.  So 
with  the  lowering  of  the  pressure  of  a  saturated  solution  super- 
saturation  will  result  and  crystals  form.  Therefore,  in  general, 
crystals  may  form  from  a  solution  by  the  evaporation  of  the 
solvent,  by  the  lowering  of  the  temperature  or  by  a  decrease  in 
pressure. 

A  crystal  is  formed  from  a  fused  mass  in  much  the  same  way 
as  from  a  solution.  The  most  familiar  example  of  crystalliza- 
tion from  fusion  is  the  formation  of  ice  crystals  when  water 
freezes.  While  we  do  not  ordinarily  consider  it  in  this  way, 
water  is  fused  ice.  When  the  temperature  is  sufficiently  lowered 
the  water  can  no  longer  remain  liquid,  and  it  becomes  solid  by 
crystallization  into  ice.  The  particles  of  water  which  were  free 
to  move  in  any  direction  in  the  liquid  now  become  fixed  in  their 
position,  and  by  the  laws  of  molecular  attraction  arrange  them- 
selves in  a  definite  order  and  build  up  a  solid  crystalline  mass. 
The  formation  of  igneous  rocks  from  molten  lavas,  while  more 


INTRODUCTION  3 

complicated,  is  similar  to  the  freezing  of  water.  In  the  fluid 
lava  we  have  many  elements  in  a  dissociated  state.  As  the 
lava  cools  these  elements  gradually  group  themselves  into  differ- 
ent mineral  molecules,  which  gather  together  and  slowly  crystal- 
lize to  form  the  mineral  particles  of  the  resulting  solid  rock. 

The  third  mode  of  crystal  formation,  that  in  which  the  crys- 
tals are  produced  from  a  vapor,  is  less  common  than  the  other 
two  described  above.  The  principles  that  underlie  the  crystal- 
lization are  much  the  same.  The  dissociated  chemical  atoms 
through  the  cooling  of  the  gas  are  brought  closer  together  until 
they  at  last  form  a  solid  with  a  definite  crystal  structure.  An  ex- 
ample of  this  mode  of  crystal  formation  is  seen  in  the  formation 
of  sulphur  crystals  about  the  mouths  of  fumeroles  in  volcanic 
'  regions,  where  they  have  been  crystallized  from  sulphur-bearing 
vapors. 

The  most  fundamental  and  important  fact  concerning  crystals 
is  that  they  possess  a  definite  internal  structure.  A  crystal  is  to 
be  conceived  as  made  up  of  an  almost  infinite  number  of  exces- 
sively minute  mineral  particles  which  have  a  regular  arrange- 
ment and  relation  to  each  other  and  form,  as  it  were,  a  crystal 
network.  Little  is  definitely  known  as  to  the  character  or  size  of 
these  mineral  particles.  They  may  be  the  same  as  the  chemical 
molecule,  but  more  probably  consist  in  definite  groups  of  that 
molecule.  There  are  many  proofs  that  a  crystal  does  possess  a 
Infinite  internal  arrangement  of  its  mineral  particles,  but  the 
following  three  are  the  most  important. 

Cleavage.  Many  minerals  when  fractured  break  with  definite 
and  smooth  flat  surfaces  which  are  known  as  cleavage  planes. 
Common  salt,  halite,  for  instance,  cleaves  in  three  different  planes 
which  are  at  right  angles  to  each  other.  It  is  said,  therefore,  to 
have  a  cubic  cleavage.  When  it  crystallizes  it  usually  shows 
cubic  forms  also.  The  planes  of  cleavage  are  found  to  be  always 
parallel  to  the  natural  cubic  crystal  faces.  If  the  internal  struc- 
ture of  halite  was  heterogeneous,  the  fact  that  it  always  shows  this 
cubical  cleavage  would  be  inexplicable.  It  can  only  be  explained 
by  assuming  some  definite  internal  arrangement  which  permits 
and  controls  such  a  cleavage. 


4  MANUAL  OF  MINERALOGY 

Optical  Properties.  All  transparent  crystals  have  definite 
effects  upon  the  light  which  passes  through  them.  Many  of 
them  further  produce  changes  in  the  character  of  the  light  which 
cannot  be  accounted  for  except  through  the  constraining  influ- 
ence of  the  internal  structure  of  the  mineral.  Take  the  case  of 
calcite  as  an  example.  In  general,  if  you  look  at  an  object  through 
a  clear  block  of  calcite  you  will  observe  a  double  image.  The 
mineral,  in  other  words,  has  the  power  of  doubly  refracting  light. 
Further,  it  can  be  proved  that  each  of  the  two  rays  into  which 
calcite  breaks  up  light  has  a  definite  plane  of  vibration,  i.e.,  each 
ray  is  polarized.  A  piece  of  glass  similar  in  shape  to  the  calcite 
block  would  not  have  produced  these  effects,  because  the  internal 
structure  of  glass  is  heterogeneous,  while  that  of  calcite  is  definite 
and  regular. 

Regular  and  Constant  Outward  Form.  If  a  series  of  objects 
all  having  the  same  shape  and  size  are  grouped  together  accord- 
ing to  some  regular  arrangement,  the  resulting  mass  will  have  a 
definite  form  which  will  bear  a  strict  relationship  to  the  char- 
acter of  the  individual  objects  and  the  law  which  was  followed 
in  assembling  them.  As  a  simple  illustration,  consider  an  ordi- 
nary pile  of  bricks.  If  each  individual  brick  is  exactly  like 
every  other  in  size  and  all  of  them  are  piled  together  according 
to  a  regular  plan,  the  shape  of  the  resulting  mass  will  depend 
directly  upon  the  shape  of  the  individual  bricks  and  the  law 
which  governed  their  arrangement.  Figs.  A  and  B,  Plate  I,  arfc 
reproductions  from  photographs  of  models  which  are  built  up 
solidly  of  small  steel  balls.  All  of  the  constituent  particles  of 
each  model  are  exactly  alike  in  shape  and  size,  and  they  have 
been  piled  together  according  to  a  regular  arrangement.  The 
result  has  been,  as  is  shown  in  the  figures,  to  produce  regularly 
and  definitely  shaped  solids.  If  therefore  a  regular  arrange- 
ment of  uniform  particles  produces  a  solid  with  a  definite  shape, 
the  converse  proposition  must  be  true.  If  we  have  a  mineral 
which  occurs  in  certain  characteristic  and  uniformly  shaped 
crystals  (halite,  for  example,  in  cubes),  it  must  follow  that  this 
could  only  be  accomplished  through  the  mineral  possessing  a 
regular  internal  structure. 


PLATE  I. 


A.    Cube. 


B.    Octahedron. 
Models  made  of  Steel  Balls. 


INTRODUCTION 


The  Outward  Crystal  Form  May  Be  Varied  with  the 
Same  Internal  Crystalline  Structure.  There  may  be  several 
different  limiting  forms  possible  upon  crystals  of  the  same  min- 
eral. Galena,  PbS,  for  example,  usually  crystallizes  in  the  form  of 
a  cube,  but  it  also  at  times  shows  octahedral  crystals.  The  in- 
ternal structure  of  galena  is  constant,  but  both  the  cube  and 
octahedron  are  forms  that  conform  to  that  structure.  The 
models  shown  on  Plate  I  illustrate  this  point.  Both  are  built 
up  of  similar  particles  and  their  arrangement  is  the  same  in  each 
case.  In  one,  however,  (Fig.  A),  the  planes  of  a  cube,  and  in 
the  other  (Fig.  B)  the  planes  of  an  octahedron,  limit  the  figure. 

With  the  same  internal  structure  there  are,  however,  only  a 
certain  number  of  possible  planes  which  can  serve  to  limit  a 
crystal.  And  it  is  to  be  noted,  B( 
moreover,  that  of  these  possible 
planes  there  are  only  a  com-  < 
paratively  few  which  commonly 
occur.  The  positions  of  the 
faces  of  a  crystal  are  deter- 
mined by  those  directions  in 
which  on  account  of  the  in-  , 
ternal  structure  a  large  number 
of  the  individual  mineral  parti- 
cles lie.  And  those  planes 
which  include  the  greater  num- 
ber of  particles  are  the  ones 
most  commonly  found  as  faces  upon  the  crystals.  Consider 
Fig.  1,  which  might  represent  one  layer  of  particles  in  a  certain 
crystal  network.  The  particles  are  equally  spaced  from  each 
other  and  have  a  rectilinear  arrangement.  It  will  be  observed 
that  there  are  several  possible  lines  through  this  network  that 
include  a  greater  or  less  number  of  the  particles.  These  lines 
would  represent  the  cutting  direction  through  this  network  of 
certain  possible  crystal  planes;  and  it  would  be  found  that  of 
these  possible  planes  those  which  include  the  larger  number 
of  particles,  like  those  cutting  along  the  lines  A-B  and  A-C, 
would  be  the  more  common  in  occurrence. 


Fig.  1. 


6 


MANUAL  OF  MINERALOGY 


Law  of  the  Constancy  of  Interfacial  Angles.  Since  the 
internal  structure  of  any  mineral  is  always  constant,  and  since 
the  possible  crystal  faces  of  that  mineral  have  a  definite  relation- 
ship to  that  structure,  it  follows  that  the  faces  must  have  also  a 
definite  relationship  to  each  other.  This  fact  may  be  stated  as 
follows:  The  angles  between  two  similar  faces  on  the  same  substance 
are  always  the  same.  Fig.  1  will  also  illustrate  this  point.  The 
face  which  cuts  the  network  along  the  line  A-C  must  make  an 
angle  of  45  degrees  with  the  face  which  cuts  along  the  line 
A-B,  etc.  This  law  is  the  most  fundamental  and  important  in 
the  science  of  crystallography.  It  frequently  enables  one  to 
identify  a  mineral  by  the  measurement  of  the  interfacial  angles 
on  its  crystals.  A  mineral  may  be  found  in  crystals  of  widely 
varying  shapes  and  sizes,  but  the  angle  between  two  similar  faces 
will  always  be  the  same. 

An  important  part  of  the  study  of  crystallography  consists 
in  the  measuring  and  classifying  of  the  interfacial  angles  on  the 
crystals  of  all  minerals.  These  measurements  are  accomplished 
by  means  of  instruments  known  as  goniometers.  For  accurate 
work,  particularly  in  the  case  of  small  crystals,  a  type  of  in- 
strument known  as  a  reflection  goniometer  is  used.  This  is  an 
instrument  upon  which  the 
crystal  to  be  measured  is 
mounted  so  as  to  reflect 
beams  of  light  from  its  faces 
through  a  telescope  to  the 
eye.  The  size  of  the  angle 
through  which  a  crystal  has 
to  be  turned  in  order  to 
throw  successive  beams  of 
light  from  two  adjacent  faces 
into  the  telescope  deter- 
mines the  angle  existing 

.     c  Fig.  2.    Contact  Goniometer. 

between  the  faces.    A  sim- 
pler instrument  used  for  approximate  work   and  with  larger 
crystals  is  known  as  a  contact  goniometer.    Its  character  and  use 
are  illustrated  by  Fig.  2. 


SYMMETRY  1 

The  regular  internal  structure  of  crystals  requires  that  the 
ultimate  individual  mineral  particles  must  be  at  least  physically 
alike.  A  physical  likeness  between  these  particles  necessitates 
that  they  should  also  be  the  same  chemically,  or  at  least  closely 
similar.  Consequently  we  can  state  that  in  general  a  crystal 
must  be  made  up  of  a  regular  assemblage  of  particles  which  are 
chemically  the  same,  and  therefore  that  a  crystallized  mineral 
must  have  a  definite  and  uniform  chemical  composition.  This 
statement  is  a  general  one  and  will  suffice  for  the  present;  certain 
modifications  will  be  found  stated  on  page  77  under  isomor- 
phism. A  crystal  is  a  guarantee  of  the  chemical  homogeneity 
of  a  mineral.  From  this  it  follows  that  only  definite  chemical 
compounds  are  capable  of  crystallization. 

To  sum  up  the  conclusions  of  the  preceding  paragraphs:  A 
crystal  is  a  solid  with  definite  chemical  composition  which  possesses 
a  definite  internal  arrangement  of  its  mineral  particles.  These 
internal  characteristics  are  expressed  outwardly  in  a  definite  external 
form.  And  since  the  internal  structure  of  the  same  substance  is 
always  constant,  the  angles  between  the  similar  bounding  planes  of 
the  crystals  of  that  substance  are  also  constant. 

II.   SYMMETRY. 

Crystals  are  grouped  together  into  different  classes  according 
to  the  symmetry  which  they  show.  The  symmetry  of  crystals 
is  of  three  kinds,  namely:  1.  Symmetry  in  respect  to  a  plane; 
2.  Symmetry  in  respect  to  a  line;  3.  Symmetry  in  respect  to  a 
point. 

Symmetry  Plane.  A  symmetry  plane  is  an  imaginary  plane 
which  divides  a  crystal  into  halves,  each  of  which  is  the  mirror 
image  of  the  other.  Fig.  3  will  illustrate  the  character  of  such 
a  plane.  The  shaded  portion  of  the  figure  shows  the  position 
of  the  one  plane  of  symmetry  that  a  crystal  of  this  sort  possesses. 
For  each  face,  edge  or  point  on  one  side  of  the  plane  there  is  a 
corresponding  face,  edge  or  point  in  a  similar  position  on  the  other 
side  of  the  plane. 

Symmetry  Axis.  A  symmetry  axis  is  an  imaginary  line 
through  a  crystal  about  which  the  crystal  may  be  revolved  as 


8 


MANUAL  OF  MINERALOGY 


upon  an  axis  and  repeat  itself  in  appearance  two  or  more  times 
during  the  revolution.  In  Fig.  4  the  line  C-Cf  is  an  axis  of 
symmetry,  for  when  the  crystal  represented  is  revolved  upon  it, 
it  will  have,  after  a  revolution  of  180°,  the  same  appearance  as 
at  first;  or  in  other  words,  similar  planes,  edges,  etc.,  will  appear 
in  the  places  of  the  corresponding  planes  and  edges  of  the 
original  position.  Point  A' will  occupy  the  original  position  of 
A,  B'  that  of  B,  etc.  Since  the  crystal  is  repeated  twice  in 
appearance  during  a  complete  revolution,  this  axis  is  said  to 
be  one  of  binary  or  twofold  symmetry.  In  addition  to  axes 
of  binary  symmetry,  we  have  axes  of  trigonal  (threefold),  tet- 
ragonal (fourfold)  and  hexagonal  (sixfold)  symmetry. 


Fig.  3. 
Symmetry  Plane. 


Fig.  4. 
Symmetry  Axis. 


Fig.  5. 

Symmetry  Center. 


Center  of  Symmetry.  A  crystal  has  a  center  of  symmetry 
if  an  imaginary  line  is  passed  from  some  point  on  its  surface 
through  its  center,  and  a  similar  point  is  found  on  the  line  at  an 
equal  distance  beyond  the  center.  The  crystal  represented  in 
Fig.  5  has  a  center  of  symmetry,  for  the  point  A  is  repeated  at 
A'  on  a  line  passing  from  A  through  the  center,  C,  of  the  crystal, 
the  distances  AC  and  A'C  being  equal. 

All  possible  crystal  forms  can  be  grouped  into  thirty-two 
classes  depending  upon  the  different  degrees  of  symmetry  which 
they  show.  These  thirty-two  classes  may  be  further  grouped 
into  six  systems,  the  classes  of  each  system  having  certain  close 


CRYSTAL  NOTATION  9 

relations  to  each  other.  These  systems  are  known  as  the  Iso- 
metric, Tetragonal,  Hexagonal,  Orthorhombic,  Monoclinic  and 
Triclinic  Systems.  All  crystals  will  be  found  to  belong  to  one  or 
the  other  of  these  systems.  As  stated  above,  there  are  thirty-two 
possible  subdivisions  of  these  six  systems,  but  the  majority  of 
them  are  only  of  theoretical  interest,  since  practically  all  known 
species  can  be  placed  in  one  or  the  other  of  some  ten  or  twelve 
classes. 

III.   CRYSTAL  -NOTATION. 

A  system  of  notation  has  been  developed  by  which  we  can 
describe  the  different  crystal  classes  and  the  crystal  forms  found 
in  each.  One  of  the  important  conceptions  to  this  end  is  that  of 
crystallographic  axes, 

Crystallographic  Axes.  Crystallographic  axes  are  imaginary 
lines  or  directions  within  a  crystal  to  which  the  crystal  faces  are 
referred  and  in  terms  of  which  they  are  described.  In  the  differ- 
ent systems  the  axes  vary  in  number  (three  or  four),  in  their 
relative  lengths  and  in  the  angles  of  inclination  to  each  other. 
As  a  general  case  we  will  consider  the  crystallographic  axes  of 
the  Orthorhombic  System.  They  are  three  in  number,  at  right 
angles  to  each  other,  and  each  has  a  characteristic  relative  length. 
Fig.  6  represents  such  axes  for  the  Orthorhombic  mineral  sulphur. 
When  placed  in  the  proper  position  for  description,  or  "orien- 
tated" as  it  is  termed,  one  axis  called  a  is  horizontal  and  per- 
pendicular to  the  observer,  another  axis,  called  6,  is  horizontal 
and  parallel  to  the  observer,  while  the  third  axis, 'called  c,  is 
vertical.  The  ends  of  each  axis  are  designated  by  either  a  plus 
or  a  minus  sign,  the  front  end  of  a,  the  right-hand  end  of  b  and 
the  upper  end  of  c  being  positive,  while  in  each  case  the  opposite 
end  is  negative.  When,  as  in  the  Orthorhombic  System,  the 
three  axes  have  different  relative  lengths,  these  values  have  to 
be  determined  experimentally  by  making  the  necessary  measure- 
ments on  crystals  of  each  mineral.  Fig.  7  would  represent  a 
crystal  of  sulphur  in  which  each  face  of  the  crystal  form,  known 
as  a  pyramid,  intercepts  each  axis  at  what  is  considered  as  its 
unit  length.  From  the  values  obtained  by  measuring  the  angles 


10 


MANUAL  OF  MINERALOGY 


between  the  different  faces  of  this  crystal  an  expression  of  the 
relative  lengths  of  the  three  axes  can  be  obtained  by  calculation. 
The  length  of  the  b  axis  is  taken  as  unity  and  the  lengths  of  the 
a  and  c  axes  are  expressed  in  terms  of  it.  The  axial  ratio  for 
sulphur  is  a  :  b  :  c  =  0.813  :  1.00  :  1.903.  It  must  be  borne  in 
mind  that  these  lengths  are  only  relative  in  their  value.  They 
do  not  represent  any  actual  distances.  A  sulphur  crystal  may 
be  of  microscopic  size  or  several  inches  in  diameter,  but  in  either 
case  the  above  ratio  would  hold  true. 


-C 

Fig.  6. 

Orthorhombic 
Crystal  Axes. 


Fig.  7. 

Orthorhombic 
Pyramid. 


i    _i        ""*!— 

lCt!,l&,ooC. 

, 

-—? 

- 

-1--—  . 

Fig.  8. 

Orthorhombic 

Prism. 

Parameters.  Crystal  faces  are  described  according  to  their 
relations  to  the  crystallographic  axes.  A  series  of  numbers  which 
indicate  the  relative  distances  by  which  a  face  intersects  the 
different  axes  are  called' its  parameters.  A  face  which  cuts  all 
three  axes  at  distances  from  the  point  of  their  intersection  which 
are  relatively  the  same  as  the  unit  lengths  of  the  axes  is  said  to 
have  the  following  parameters:  la,  16,  Ic  (see  Fig.  7).  A  face 
which  cuts  the  two  horizontal  axes  at  distances  which  are  rela- 
tively to  each  other  as  the  unit  lengths  of  those  axes  but  is  paral- 
lel to  the  vertical  axis  would  have  for  parameters  la,  16,  ooc  (see 
Fig.  8).  If  a  face  cuts  the  two  horizontal  axes  at  distances 
proportional  to  their  unit  lengths  and  cuts  the  vertical  axis  at 


CRYSTAL  NOTATION 


11 


a  distance  twice  its  relative  unit  length,  it  will  have  for  param- 
eters la,  16,  2c.  It  is  to  be  emphasized  that  these  parameters 
are  strictly  relative  in  their  values  and  do  not  indicate  any 
actual  cutting  lengths.  To  further  illustrate  this,  consider 
Fig.  9,  which  represents  a  possible  sulphur  crystal.  The  forms 
present  upon  it  are  two  pyramids 
of  different  slope  but  each  inter- 
secting all  three  of  the  crystal  axes 
when  properly  extended.  The  lower 
pyramid  intersects  the  two  hori- 
zontal axes  at  distances  which  are 
proportional  to  their  unit  lengths  _ 
and  if  it  was  extended  as  shown  by 
the  dotted  lines  would  also  cut  the 
vertical  axis  at  a  distance  propor- 
tional to  its  unit  length.  The  pa- 
rameters of  the  face  of  this  form 
which  cuts  the  positive  ends  of  the 
three  axes  would  be  la,  16,  Ic. 
The  upper  pyramid  would  cut  the 
two  horizontal  axes,  as  shown  by  the  dotted  lines,  also  at  dis- 
tances which,  although  greater  than  in  the  case  of  the  lower 
pyramid,  are  still  proportional  to  their  unit  lengths.  It  cuts  the 
vertical  axis,  however,  at  a  distance  which,  when  considered  in 
respect  to  its  intersections  with  the  horizontal  axes,  is  propor- 
tional to  one-half  of  the  unit  length  of  c.  The  parameters  of  a 
face  of  this  form  would  therefore  be  la,  16,  %c.  From  this  ex- 
ample it  will  be  seen  that  the  parameters  la,  16,  do  not  in  the  two 
cases  represent  the  same  actual  cutting  distances  but  express  only 
relative  values.  The  parameters  of  a  face  do  not  in  any  way 
determine  its  size,  for  a  face  may  be  moved  parallel  to  itself  for 
any  distance  without  changing  the  relative  values  of  its  intersec- 
tions with  the  crystallographic  axes. 

Law  of  Definite  Mathematical  Ratio.  It  is  to  be  noted  that 
in  general  the  ratio  of  the  intercepts  of  a  crystal  face  upon  the 
crystallographic  axes  can  be  expressed  by  whole  numbers  or 
definite  fractions.  These  numbers,  or  fractions,  are  commonly 


Fig.  9. 


12  MANUAL  OF  MINERALOGY 

simple,  such  as  1,  2,  3,  |,  %,  f ,  etc.,  and  in  the  great  majority  of 
cases  are  1  or  oo.  This  law,  that  the  axial  intercepts  of  all 
crystal  faces  form  a  definite  mathematical  ratio,  is  an  extremely 
important  one.  It  is  a  necessary  corollary  to  the  theoretical 
considerations  given  on  page  5  and  following. 

Indices.  Various  methods  of  notation  have  been  devised  to 
express  the  intercepts  of  any  crystal  face  upon  the  crystal  axes, 
and  several  different  ones  are  in  common  use.  The  most  uni- 
versally employed  is  the  system  of  indices  of  Miller.  While  not 
as  simple  for  a  beginner,  perhaps,  as  some  one  of  the  systems  in 
which  the  parameters  of  the  crystal  faces  are  used,  it  adapts  itself 
so  much  more  readily  to  crystallographic  calculations  and  con- 
sequently has  so  wide  a  use  that  it  seems  wise  to  introduce  it  here. 

The  indices  of  a  face  consist  of  a  series  of  whole  numbers  which 
have  been  derived  from  its  parameters  by  their  inversion  and,  if 
necessary,  the  subsequent  clearing  of  fractions.  The  indices  of 
a  face  are  always  given,  so  that  the  three  numbers  refer  to  the 
a,  b  and  c  axes  respectively,  and  therefore  ordinarily  the  letters 
which  indicate  the  different  axes  are  omitted.  The  pyramid 
illustrated  in  Fig.  7,  which  has  la,  Ib,  Ic  for  parameters,  would 
have  111  for  indices.  The  face,  Fig.  8,  which  has  la,  16,  ooc 
for  parameters,  would  have  110  for  indices.  The  face,  Fig.  9, 
which  has  la,  16,  |c  for  parameters,  would  have  112  for  indices. 
A  face  which  has  la,  16,  2c  for  parameters  would  have  221  for 
indices. 

Common  use  is  made  of  what  is  known  as  the  symbol  of  a 
form.  A  symbol  of  any  form  consists  of  the  indices  of  the  face 
having  the  simplest  relations  to  the  axes.  This  is  used  when 
it  is  desired  to  refer  to  some  particular  crystal  form,  and  the  sym- 
bol then  stands  for  the  whole  form  and  not  simply  for  the  single 
face  whose  indices  it  is. 

IV.   DEFINITIONS   OF   VARIOUS   TERMS. 

Crystal  Form.  By  the  expression  " crystal  form"  is  meant 
the  assemblage  of  all  similar  faces  which  are  possible  with  a 
certain  degree  of  symmetry.  In  Fig.  7  is  represented  a  crystal 
form  known  as  a  pyramid.  In  the  particular  symmetry  class 


DEFINITIONS  OF  VARIOUS   TERMS 


13 


to  which  it  belongs  the  three  crystal  axes  are  axes  of  binary 
symmetry  and  the  axial  planes  are  planes  of  symmetry.  Under 
these  conditions,  if  we  assume  the  presence  of  the  face  A  we  must 
have  the  other  seven  faces  also  in  order  to  satisfy  the  demands 
of  the  symmetry.  In  this  case  the  assemblage  of  the  eight 
pyramidal  faces  constitutes  the  crystal  form.  A  crystal  form 
does  not  necessarily  make  a  solid 
figure.  Consider  Fig.  10,  which  is 
of  a  crystal  of  the  Monoclinic  Sys- 
tem. In  this  system  the  b  axis  is 
an  axis  of  binary  symmetry  and  the 
plane  of  the  a  and  c  axes  is  a  sym- 
metry plane.  Under  these  condi- 
tions, if  we  assume  the  presence  of 
the  plane  6,  the  symmetry  demands 
only  the  parallel  face  b'.  So  these 
two  faces,  being  all  the  possible 
similar  planes  with  this  particular 
symmetry,  constitute  a  crystal  form, 
forms  present  on  the  crystal  represented  in  Fig.  10. 

Crystal  Habit.  By  the  crystal  habit  of  any  mineral  is  meant 
the  common  and  characteristic  form  or  combination  of  forms  in 
which  that  mineral  crystallizes.  Galena,  for  example,  has  a  cubic, 
magnetite  an  octahedral  and  garnet  a  dodecahedral  habit.  By 
this  is  meant  that,  although  these  minerals  are  found  in  crys- 
tals which  show  other  forms,  such  occurrences  are  comparatively 
rare,  and  their  "habit"  is  to  crystallize  as  indicated. 

Crystal  Combinations.  In  the  great  majority  of  cases,  a 
crystal  will  show  a  combination  of  two  or  more  crystal  forms 
rather  than  one  single  form.  In  fact,  many  crystal  forms,  since 
they  do  not  make  a  solid  figure  by  themselves,  must  occur  in 
combination  with  other  forms.  The  combination  in  which  it 
occurs  may  quite  change  the  appearance  of  a  forrn,  and  its  recog- 
nition will  depend  upon  the  position  and  relation  of  its  faces 
rather  than  upon  their  shape.  Fig.  11  is  of  a  simple  form  known 
as  a  cube,  and  Fig.  12  is  of  a  simple  form  known  as  an  octahedron. 
Fig.  13  shows  a  combination  of  the  two,  in  which  the  corners  of 


Fig.  10. 

There  are  three  crystal 


14 


MANUAL  OF  MINERALOGY 


the  cube  are  truncated  by  the  faces  of  the  octahedron,  while 
Fig.  14  shows  the  same  two  forms  in  a  combination  in  which 
the  points  of  the  octahedron  are  truncated  by  the  faces  of  the 
cube.  When  a  corner  or  an  edge  of  one  form  is  replaced  by  a 
face  of  another  form,  the  first  is  said  to  be  truncated  by  the 
second.  If  an  edge  is  replaced  by  two  similar  faces  it  is  said  to 
be  beveled. 


^        a     - 

X 

a 

a 

s'' 

^^ 

Fig.  11. 
Cube. 

Fig.  13.  Fig.  14. 

Cube  Truncated    Octahedron  Trun- 
by  Octahedron.        cated  by  Cube. 

Crystal  Distortion.  It  seldom  happens  that  the  conditions 
for  crystal  growth  are  such  as  to  permit  the  development  of 
crystals  of  ideal  symmetry.  The  crystal  may  have  grown  more 
rapidly  in  one  direction  than  in  another;  other  surrounding  min- 
erals may  have  interfered,  and  in  various  ways  its  symmetrical 
growth  been  prevented.  Such  a  crystal  is  said  to  show  distortion. 


Fig.  15.    Cube.  Fig.  16.  Distorted  Cube.     Fig.  17.    Octahedron. 

Ordinarily  the  amount  of  distortion  is  not  so  great  as  to  prevent 
one  from  readily  imagining  what  the  ideally  developed  crystal 
would  be  like  and  so  determining  its  symmetry  and  character. 
It  is  to  be  noted  that  the  real  symmetry  of  a  crystal  does  not 
depend  upon  the  symmetrical  shape  and  size  of  its  faces,  but 
rather  upon  the  symmetrical  arrangement  of  its  interfacial 


DEFINITIONS  OF   VARIOUS   TERMS  15 

angles.     In  the  Figs.  15  and  16,  17  and  18,  19  and  20,  are  given 
various  crystal  forms,  first  ideally  developed  and  then  distorted. 


Fig.  18.  Fig.  19.  Fig.  20. 

Distorted  Octahedron.  Dodecahedron.         Distorted  Dodecahedron. 

Crystal  Pseudomorphs.  At  times  we  find  a  mineral  occur- 
ring in  crystals  which  prove  to  be  not  the  characteristic  forms 
for  that  mineral,  but  are  rather  the  typical  forms  of  some  other 
species.  Such  crystals  are  said  to  be  pseudomorphs,  or  false 
forms.  They  originate  in  various  ways.  The  mineral  may  have 
changed  in  its  composition  without,  however,  changing  its  crystal 
form.  We  find,  for  example,  that  cuprite,  Cu20,  frequently 
alters  to  malachite,  CuC03.Cu(OH)2,  but  without  a  change 
in  the  crystal  shape.  The  resulting  crystals  would  have  the 
composition  of  malachite  but  the  crystal  form  of  cuprite.  An- 
other mode  of  origin  is  to  have  one  mineral  deposited  on  the 
crystals  of  another  and  so  form,  as  it  were,  a  cast  of  the  second. 
Smithsonite,  ZnC03,  is  at  times  found  in  pseudomorphic  crystals 
whose  forms  are  those  of  calcite.  In  this  case  the  smithsonite 
has  been  deposited  in  a  thin  layer  over  the  crystal  of  calcite, 
which  may  have  subsequently  been  removed.  The  resulting 
crystal  is  a  pseudomorph  of  smithsonite  after  calcite.  Pseudo- 
morphs cannot  be  regarded  as  true  crystals,  since  their  internal 
structure  does  not  correspond  to  the  outward  crystal  form. 

Twin  Crystals.  When  two  or  more  crystals  intergrow  accord- 
ing to  some  definite  law,  the  resulting  group  is  said  to  be  a  twin 
crystal.  The  different  members,  ordinarily  two,  of  a  twin 
crystal  have  usually  a  plane,  known  as  a  twinning  plane,  or  an 
axis,  known  as  a  twinning  axis,  which  is  common  to  both.  In 
Fig.  21,  which  represents  a  twin  crystal  of  fluorite,  we  have  two 
cubes  intergrown  in  such  a  way  that  the  diagonal  axis  A-A'  is 


16 


MANUAL  OF  MINERALOGY 


common  to  the  two  individuals.  The  individual,  the  faces  of 
which  are  shaded  in  the  figure,  lies  as  if  it  had  been  turned  about 
this  axis  from  the  position  occupied  by  the  other  individual 
through  an  angle  of  60  degrees.  The  line  A- A'  is  known  as  the 
twinning  axis.  Tn  Fig.  22  is  represented  a  twinned  octahedron. 
The  two  individuals  here  are  grown  together  with  an  octahedral 


Fig.  21.    Twinned  Cubes. 


Fig.  22.    Twinned  Octahedron. 


face  in  common.  It  will  be  noted  that  the  composition  plane, 
which  is  shaded,  is  parallel  to  one  face  of  each  individual.  This 
plane  is  known  as  the  twinning  plane.  The  twin  of  Fig.  21  is 
known  as  a  penetration  twin,  since  the  two  individuals  inter- 
penetrate each  other;  while  the  twin  of  Fig.  22  is  a  contact  twin, 
since  the  two  individuals  lie  simply  in  contact  with  each  other 
upon  a  certain  plane. 

V.  ISOMETRIC   SYSTEM. 

Crystallographic  Axes.  The  crystallographic  axes  of  the  Iso- 
metric System  are  three  in  number,  of  equal  lengths,  and  make 
right  angles  with  each  other.  When 
properly  orientated  one  axis  is  vertical 
and  the  other  two  are  horizontal,  one 
a2  being  parallel  and  the  other  perpendicu- 
lar to  the  observer,  as  is  shown  in  Fig. 
23.  Since  the  three  axes  are  identical 
in  character,  they  are  interchangeable, 
and  any  one  of  them  may  serve  as  the 
vertical  axis,  etc.  In  giving  the  indices 
of  a  face  of  an  isometric  form,  the  order  of  the  axes,  etc.,  is  the 
same  as  described  in  a  previous  paragraph,  page  9. 


-0,2 


-Cti 


-ct8 
Fig.  23.     Isometric  Axes. 


ISOMETRIC  SYSTEM 


17 


Normal  CJass. 

Symmetry  and  Forms.  The  symmetry  shown  by  the  crys- 
tals of  the  Normal  Class  of  the  Isometric  System  is  as  follows. 
The  three  crystallographic  axes  are  axes  of  tetragonal  symmetry 
(see  Fig.  24).  There  are  also  four  diagonal  axes  of  trigonal  sym- 
metry. These  axes  emerge  in  the  middle  of  each  of  the  octants 
formed  by  the  intersection  of  the  crystallographic  axes  (see 
Fig.  25).  Further,  there  are  six  diagonal  axes  of  binary  sym- 
metry, each  of  which  bisects  one  of  the  angles  between  two  of 
the  crystallographic  axes,  as  illustrated  in  Fig.  26. 


Fig.  25.  Fig.  26. 

Axes  of  Symmetry,  Isometric  System,  Normal  Class. 


-Ct3 


Fig.  27.  Fig.  28. 

Planes  of  Symmetry,  Isometric  System,  Normal  Class. 

This  class  shows  nine  planes  of  symmetry,  three  of  them  being 
known  as  the  axial  planes,  since  each  includes  two  crystallo- 
graphic axes  (see  Fig.  27),  and  six  being  called  diagonal  planes, 
since  each  bisects  the  angle  between  two  of  the  axial  planes 
(see  Fig.  28). 


18 


MANUAL  OF  MINERALOGY 


To  summarize  the  symmetry  of  this  class: 

3  crystallographic  axes  of  tetragonal  symmetry; 

4  diagonal  axes  of  trigonal  symmetry; 
6  diagonal  axes  of  binary  symmetry; 
3  axial  planes  of  symmetry; 

6  diagonal  planes  of  symmetry. 

This  symmetry,  which  is  of  the  highest  degree  possible  in 
solids  with  plane  surfaces,  defines  the  Normal  Class  of  the  Iso- 
metric System.  Every  crystal  form  and  every  combination  of 
forms  that  belongs  to  this  class  must  show  its  complete  sym- 
metry. It  is  important  to  remember  that  in  this  class  the  three 
crystallographic  axes  are  axes  of  tetragonal  symmetry,  since  this 
fact  distinguishes  the  class  from  all  others  and  by  means  of  it  the 
crystallographic  axes  can  be  easily  located  and  a  crystal  properly 
orientated. 

The  forms  of  the  Isometric  System,  Normal  Class,  are  as 
follows: 

1.  Cube  or  Hexahedron.  The  cube  is  a  form  composed  of  six 
square  faces  which  make  90°  angles  with  each  other,  Each  face 
intersects  one  of  the  crystallographic  axes  and  is  parallel  to  the 
other  two.  Its  symbol  is  (100).  Fig.  29  represents  a  simple  cube. 


a  ,001 


100    > 

_ 


a 

i       ! 
j [__. 


010 
— a 


Fig.  29.    Cube.  Fig.  30.    Octahedron. 

2.  Octahedron.  The  octahedron  is  a  form  composed  of  eight 
equilateral  triangular  faces,  each  of  which  intersects  all  three  of 
the  crystallographic  axes  equally.  Its  symbol  is  (111).  Fig.  30 
represents  a  simple  octahedron  and  Figs.  31  and  32  show  com- 
binations of  a  cube  and  an  octahedron.  When  in  combination 


ISOMETRIC  SYSTEM 


19 


the  octahedron  is  to  be  recognized  by  its  eight  similar  faces,  each 
of  which  is  equally  inclined  to  the  three  crystallographic  axes. 
It  is  to  be  noted  that  the  faces  of  an  octahedron  truncate  sym- 
metrically the  corners  of  a  cube. 


\/ 


Fig.  31. 
Cube  and  Octahedron. 


Fig.  32. 
Octahedron  and  Cube. 


Fig.  33. 
Dodecahedron. 


3.  Dodecahedron.  The  dodecahedron  is  a  form  composed  of 
twelve  rhombic-shaped  faces.  Each  face  intersects  two  of  the 
crystallographic  axes  equally  and  is  parallel  to  the  third.  Its 
symbol  is  (110).  Fig.  33  shows  a  simple  dodecahedron,  Fig.  34 
shows  a  combination  of  dodecahedron  and  cube,  Figs.  35  and  36 
combinations  of  dodecahedron  and  octahedron,  and  Fig.  37  a 
combination  of  cube,  octahedron  and  dodecahedron.  It  is  to  be 
noted  that  the  faces  of  a  dodecahedron  truncate  the  edges  of 
both  the  cube  and  the  octahedron. 


«i 


Fig.  34. 
Cube  and  Dodecahedron. 


Fig.  35. 
Octahedron  and  Dodecahedron. 


4.  Tetrahexahedron.  The  tetrahexahedron  is  a  form  com- 
posed of  twenty-four  isosceles  triangular  faces,  each  of  which  in- 
tersects one  axis  at  unity,  the  second  at  some  multiple,  and  is 


20 


MANUAL  OF  MINERALOGY 


parallel  to  the  third.  There  are  a  number  of  tetrahexahedrons 
which  differ  from  each  other  in  respect  to  the  inclination  of 
their  faces.  Perhaps  the  one  most  common  in  occurrence  has 
the  parameter  relations  la,  2b,  <x>c,  the  symbol  of  which  would 
be  (210).  The  symbols  of  other  forms  are  (310),  (410),  (320), 
etc.  It  is  helpful  to  note  that  the  tetrahexahedron,  as  its  name 
indicates,  is  like  a  cube,  the  faces  of  which  have  been  replaced  by 
four  others.  Fig.  38  shows  a  simple  tetrahexahedron  and  Fig.  39 
a  cube  with  its  edges  beveled  by  the  faces  of  a  tetrahexahedron. 


*<r\  ._. 

(-\ 

'  Vf      d           /    n  > 

ly 

|                        [ 

a            d 

j 


Fig.  36.  Fig.  37. 

Dodecahedron  and  Octahedron.  Cube,  Octahedron  and  Dodecahedron. 


Fig.  38. 
Tetrahexahedron. 


Fig.  39. 
Cube  and  Tetrahexahedron. 


5.  Trapezohedron  or  Tetragonal  Trisoctahedron.  The  trapezo- 
hedron  is  a  form  composed  of  twenty-four  trapezium-shaped 
faces,  each  of  which  intersects  one  of  the  crystallographic  axes 
at  unity  and  the  other  two  at  equal  multiples.  There  are  vari- 
ous trapezohedrons  with  their  faces  having  different  angles  of 
inclination.  A  common  trapezohedron  has  for  its  parameters 


ISOMETRIC  SYSTEM 


21 


la,  26,  2c,  the  symbol  for  which  would  be  (211).  The  symbols 
for  other  trapezohedrons  are  (311),  (411),  (322),  etc.  It  will  be 
noted  that  a  trapezohedron  is  an  octahedral-like  form  and  may 
be  conceived  of  as  an  octahedron,  each  of  the  planes  of  which  has 
been  replaced  by  three  faces.  Consequently  it  is  sometimes 
called  a  tetragonal  trisoctahedron.  The  qualifying  word,  tet- 
ragonal, is  used  to  indicate  that  each  of  its  faces  has  four  edges 
and  to  distinguish  it  from  the  other  trisoctahedral  form,  the 


Fig.  40. 
Trapezohedron. 


Fig.  41. 
Dodecahedron  and  Trapezohedron. 


Fig.  42. 
Dodecahedron  and  Trapezohedron. 


Fig.  43. 
Cube  and  Trapezohedron. 


description  of  which  follows.  Trapezohedron  is  the  name,  how- 
ever, most  commonly  used.  The  following  are  aids  to  the  recog- 
nition of  the  form  when  it  occurs  in  combinations:  the  three 
similar  faces  to  be  found  in  each  octant;  the  relations  of  each 
face  to  the  axes;  and  the  fact  that  the  middle  edges  between  the 
three  faces  in  any  one  octant  go  toward  points  which  are  equi- 
distant from  the  ends  of  the  two  adjacent  crystallographic  axes. 
Fig.  40  shows  a  simple  trapezohedron,  and  Figs.  41  and  42  show 


22 


MANUAL  OF  MINERALOGY 


each  a  trapezohedron  in  combination  with  a  dodecahedron.  It 
is  to  be  noted  that  the  faces  of  the  common  trapezohedron  (211) 
(Fig.  41)  truncate  the  edges  of  the  dodecahedron.  Fig.  43  shows 
a  combination  of  cube  and  trapezohedron. 

6.  Trisoctahedron  or  Trigonal  Trisoctahedron.  The  trisocta- 
hedron  is  a  form  composed  of  twenty-four  isosceles  triangular 
faces,  each  of  which  intersects  two  of  the  crystallographic  axes 
at  unity  and  the  third  axis  at  some  multiple.  There  are  various 
trisoctahedrons  the  faces  of  which  have  different  inclinations. 
A  common  trisoctahedron  has  for  its  parameters  la,  16,  2c,  its 
symbol  being  (221).  Other  trisoctahedrons  have  the  symbols 
(331),  (441),  (332),  etc.  It  is  to  be  noted  that  the  trisoctahedron, 
like  the  trapezohedron,  is  a  form  that  may  be  conceived  of  as  an 
octahedron,  each  face  of  which  has  been  replaced  by  three  others. 
Frequently  it  is  spoken  of  as  the  trigonal  trisoctahedron,  the 
modifying  word  indicating  that  its  faces  have  each  three  edges 
and  so  differ  from  those  of  the  trapezohedron.  But  when  the 
word  "trisoctahedron"  is  used  alone  it  refers  to  this  form.  The 
following  points  would  aid  in  its  identification  when  it  is  found 
occurring  in  combinations:  the  three  similar  faces  in  each  octant; 
their  relations  to  the  axes;  and  the  fact  that  the  middle  edges 
between  them  go  toward  the  ends  of  the  crystallographic  axes. 


Fig.  44. 
Trisoctahedron. 


Fig.  45. 
Octahedron  and  Trisoctahedron. 


Fig.  44  shows  the  simple  trisoctahedron  and  Fig.  45  a  combina- 
tion of  a  trisoctahedron  and  an  octahedron.  It  will  be  noted 
that  the  faces  of  the  trisoctahedron  bevel  the  edges  of  the  octa- 
hedron. 


ISOMETRIC  SYSTEM 


23 


7.  Hexoctahedron.  The  hexoctahedron  is  a  form  composed  of 
forty-eight  triangular  faces,  each  of  which  cuts  differently  on  all 
three  crystallographic  axes.  There  are  several  hexoctahedrons, 
which  have  varying  ratios  of  intersection  with  the  axes.  A 
common  hexoctahedron  has  for  its  parameter  relations  la,  16, 
3c,  its  symbol  being  (321).  Other  hexoctahedrons  have  the 
symbols  (421),  (531),  (432),  etc.  It  is  to  be  noted  that  the  hex- 


Fig.  46. 
Hexoctahedron. 


Fig.  47. 
Cube  and  Hexoctahedron, 


Fig.  48. 
Dodecahedron  and  Hexoctahedron. 


Fig.  49. 

Dodecahedron,  Trapezohedron  and 
Hexoctahedron. 


octahedron  is  a  form  that  may  be  considered  as  an  octahedron, 
each  face  of  which  has  been  replaced  by  six  others.  It  is  to  be 
recognized  when  in  combination  by  the  facts  that  there  are  six 
similar  faces  in  each  octant  and  that  each  face  intercepts  the 
three  axes  differently.  Fig.  46  shows  a  simple  hexoctahedron, 
Fig.  47  a  combination  of  cube  and  hexoctahedron,  Fig.  48  a 
combination  of  dodecahedron  and  hexoctahedron,  and  Fig.  49  a 
combination  of  dodecahedron,  trapezohedron  and  hexoctahedron. 


24 


MANUAL  OF  MINERALOGY 


Occurrence  of  the  Above  Forms.  The  cube,  octahedron  and 
dodecahedron  are  the  most  common  of  the  isometric  forms. 
The  trapezohedron  is  also  frequently  observed  on  a  few  min- 
erals. The  other  forms,  the  tetrahexahedron,  trisoctahedron  and 
hexoctahedron,  are  rare  and  are  ordinarily  to  be  observed  only 
as  small  truncations  in  combinations. 

The  following  is  a  list  of  the  commoner  minerals  upon  the 
crystals  of  which  each  form  is  prominent: 

Cube:  Galena,  halite,  sylvite,  fluorite,  cuprite. 

Octahedron:   Spinel,  magnetite,  franklinite,  chromite. 

Dodecahedron:   Magnetite,  garnet. 

Trapezohedron:   Leucite,  garnet,  analcite. 

Pyritohedral  Class. 

The  Pyritohedral  Class  is  one  of  the  subordinate  divisions  of 
the  Isometric  System.  It  differs  from  the  Normal  Class,  since 
its  crystals  commonly  show  forms  that  do  not  possess  as  high 
a  symmetry  as  those  of  that  class.  The  name  of  the  class  is 
derived  from  that  of  its  chief  member,  pyrite. 

Symmetry  and  Forms.  The  symmetry  of  the  Pyritohedral 
Class  is  as  follows:  The  three  crystal  axes  are  axes  of  binary 


Fig.  50.  Fig.  51. 

Symmetry  of  Pyritohedral  Class,  Isometric  System. 

symmetry;  the  four  diagonal  axes,  each  of  which  emerges  in  the 
middle  of  an  octant,  are  axes  of  trigonal  symmetry;  the  three 
axial  planes  are  planes  of  symmetry  (see  Figs.  50  and  51). 

The  characteristic  forms  of  the  Pyritohedral  Class  are  as 
follows: 


ISOMETRIC  SYSTEM 


25 


1.  Pyriiohedron  or  Pentagonal  Dodecahedron.  This  form  con- 
sists of  twelve  pentagonal-shaped  faces,  each  of  which  intersects 
one  crystallographic  axis  at  unity,  the  second  axis  at  some  mul- 
tiple, and  is  parallel  to  the  third.  There  are  a  number  of  pyrito- 
hedrons  which  differ  from  each  other  in  respect  to  the  inclination 
of  their  faces.  Perhaps  the  most  common  in  occurrence  has 
the  parameter  relations  la,  26,  ooc,  the  symbol  of  which  would 
be  (210)  (see  Fig.  52).  It  is  to  be  noted  that  the  parameter  rela- 
tions of  the  pyritohedron  are  the  same  as  those  of  the  tetra- 
hexahedron  (see  page  19).  A  pyritohedron  may  be  considered 
as  derived  from  a  corresponding  tetrahexahedron  by  the  omission 
of  alternate  faces  and  the  extension  of  those  remaining.  Fig.  53 


Fig.  52. 
Pyritohedron. 


Fig.  53. 

Showing  Relation  between  Pyrito- 
hedron and  Tetrahexahedron. 


shows  the  relations  of  the  two  forms,  the  shaded  faces  of  the 
tetrahexahedron  being  those  which  when  extended  would  form 
the  faces  of  the  pyritohedron. 

2.  Diploid.  The  diploid  is  a  rare  form  found  only  in  this 
class.  It  is  composed  of  twenty-four  faces  which  correspond 
to  one-half  the  faces  of  a  hexoctahedron.  Fig.  54  represents  a 
diploid. 

In  addition  to  the  two  forms  described  above,  minerals  of 
this  class  show  also  the  cube,  octahedron,  dodecahedron,  trapezo- 
hedron  and  trisoctahedron.  Sometimes  these  forms  may  appear 
alone  and  so  perfectly  developed  that  they  cannot  be  told  from 
the  forms  of  the  Normal  Class.  This  is  often  true  of  octahedrons 
of  pyrite.  Usually,  however,  they  will  show  by  the  presence  of 
striation  lines  or  etching  figures  that  they  do  not  possess  the 


26 


MANUAL  OF  MINERALOGY 


high  symmetry  of  the  Normal  Class  but  conform  rather  to  the 
symmetry  of  the  Pyritohedral  Class.  This  is  shown  in  Fig.  55, 
which  represents  a  cube  of  pyrite  with  characteristic  striations, 
which  are  so  disposed  that  the  crystal  shows  the  lower  symmetry. 


Fig.  54.    Diploid. 


Fig.  55.    Striated  Cube. 


Fig.  56.    Cube  and  Pyritohedron.          Fig.  57.    Octahedron  and  Pyritohedron. 


Fig.  58. 
Octahedron  and  Pyritohedron. 


Fig.  59. 
Pyritohedron  and  Octahedron. 


Fig.  56  represents  a  combination  of  cube  and  pyritohedron,  in 
which  it  will  be  noted  that  the  faces  of  the  pyritohedron  truncate 
unsymmetrically  the  edges  of  the  cube.  Figs.  57,  58  and  59 
represent  combinations  of  pyritohedron  and  octahedron  with 


ISOMETRIC  SYSTEM 


27 


various  developments.  Fig.  60  shows  a  cube  truncated  with 
pyritohedron  and  octahedron.  Fig.  61  represents  a  combination 
of  cube  and  the  diploid  /  (421).  These  figures  should  be  studied 
in  order  to  impress  upon  one's  mind  the  characteristic  symmetry 
of  the  class. 


Fig.  60. 
Pyritohedron,  Cube  and  Octahedron. 


Fig.  61. 
Diploid  and  Cube. 


The  chief  mineral  of  the  Pyritohedral  Class  is  pyrite;  other  much 
.  rarer  members  are  smaltite,  chloanthite,  cobaltite,  gersdorfBte  and 
sperrylite. 

Tetrahedral  Class. 

Another  subordinate  division  of  the  Isometric  System  is  known 
as  the  Tetrahedral  Class,  deriving  its  name  from  its  chief  form, 
the  tetrahedron. 


Fig.  62.  Fig.  63. 

Symmetry  of  Tetrahedral  Class,  Isometric  System. 

Symmetry  and  Forms.  The  symmetry  of  this  class  is  as 
follows:  The  three  crystal! ographic  axes  are  axes  of  binary  sym- 
metry; the  four  diagonal  axes  are  axes  of  trigonal  symmetry; 
there  are  six  diagonal  planes  of  symmetry  (see  Figs.  62  and  63). 


28 


MANUAL  OF  MINERALOGY 


The  characteristic  forms  of  the  Tetrahedral  Class  are  as  fol- 
lows: 

1.    Tetrahedron.      The  tetrahedron   is  a  form   composed  of 
four  equilateral  triangular  faces,  each  of  which  intersects  all  of 

the  crystallographic  axes  at  equal 
lengths.  It  can  be  considered  as 
derived  from  the  octahedron  of  the 
Normal  Class  by  the  omission  of  the 
alternate  faces  and  the  extension  of 
the  others,  as  shown  in  Fig.  64. 
This  form,  shown  also  in  Fig.  65,  is 
known  as  the  positive  tetrahedron 
and  has  for  its  symbol  (111).  If 
the  other  four  faces  of  the  octa- 
hedron had  been  extended,  the 
tetrahedron  resulting  would  have 
had  a  different  orientation,  as  shown  in  Fig.  66.  This  is  known 
as  the  negative  tetrahedron  and  has  for  its  symbol  (111).  The 


Fig.  64. 

Showing  Relation  between  Octa- 
hedron and  Tetrahedron. 


Fig.  65. 
Positive  Tetrahedron. 


Fig.  66. 
Negative  Tetrahedron. 


Fig.  67. 

Positive  and  Negative 

Tetrahedrons. 


positive  and  negative  tetrahedrons  when  occurring  alone  are 
geometrically  identical,  and  the  only  reason  for  recognizing  the 
possibility  of  the  existence  of  two  different  orientations  lies  in 
the  fact  that  at  times  they  may  occur  truncating  each  other, 
as  shown  in  Fig.  67.  If  a  positive  and  negative  tetrahedron 
occurred  together  with  equal  development,  the  resulting  crystal 
could  not  be  distinguished  from  an  octahedron,  unless,  as  is 
usually  the  case,  the  faces  of  the  two  forms  showed  different  lus- 
ters, etchings  or  striations  that  would  serve  to  differentiate  them. 


ISOMETRIC  SYSTEM 


29 


Other  possible  but  rare  tetrahedral  forms  are  the  following: 
The  tristetrahedron  (Fig.  68),  the  faces  of  which  correspond  to 
one-half  the  faces  of  a  trapezohedron ;  the  deltoid  dodecahedron 
(Fig.  69),  the  faces  of  which  correspond  to  one-half  those  of 
the  trisoctahedron ;  the  hexakistetrahedron  (Fig.  70),  the  faces 
of  which  correspond  to  one-half  the  faces  of  the  hexoctahedron. 


Fig.  68. 
Tristetrahedron. 


Fig.  69. 
Deltoid  Dodecahedron. 


Fig.-  70. 

Hexakistetrahedron. 


Fig.  71. 
Cube  and  Tetrahedron. 


Fig.  72. 
Tetrahedron  and  Cube. 


Fig.  73. 
Tetrahedron  and  Dodecahedron. 


Fig.  74. 
Dodecahedron,  Cube  and  Tetrahedron. 


The  cube  and  dodecahedron  are  also  found  on  minerals  of  the 
Tetrahedral  Class.    Figs.  71  and  72  show  combinations  of  cube 


30  MANUAL  OF  MINERALOGY 

and  tetrahedron.  It  will  be  noted  that  the  tetrahedron  faces 
truncate  the  alternate  corners  of  the  cube,  or  that  the  cube  faces 
truncate  the  edges  of  a  tetrahedron.  Fig.  73  shows  the  com- 
bination of  tetrahedron  and  dode- 
cahedron. Fig.  74  represents  a 
combination  of  cube,  dodecahedron 
and  tetrahedron.  Fig.  75  shows  a 
combination  of  tetrahedron  and 
tristetrahedron. 

Tetrahedrite  and  the  related  ten- 
nantite  are  the  only  common  min- 
erals that  ordinarily  show  distinct 

Fig.  75.    Tetrahedron  and  J 

Tristetrahedron.  tctrahedral  forms.     Sphalerite  oc- 

casionally exhibits  them,  but  commonly  its  crystals  are  quite 
complex  and  distorted. 

Characteristics  of  Isometric  Crystals. 

The  striking  characteristics  of  isometric  crystals  which  would 
aid  in  their  recognition  may  be  summarized  as  follows: 

The  crystals  are  equidimensional  in  three  directions  at  right 
angles  to  each  other.  These  three  directions  in  crystals  of  the 
Normal  Class  are  axes  of  tetragonal  symmetry.  The  crystals 
commonly  show  faces  that  are  squares  or  equilateral  triangles 
or  these  figures  with  truncated  corners.  They  are  characterized 
by  the  large  number  of  similar  faces,  the  smallest  number  on 
any  form  of  the  Normal  Class  being  six.  Every  form  by  itself 
would  make  a  solid. 

Important  Isometric  Angles.  Below  are  given  various  inter- 
facial  angles  which  may  assist  in  the  recognition  of  the  commoner 
isometric  forms: 

Cube  (100)  A  cube  (010)  =  90°  O'_0". 

Octahedron  (111)  A  octahedron  (111)  =  70°  31'  44". 

Dodecahedron  (110)  A  dodecahedron  (101)  =  60°  0'  0". 

Cube  (100)  A  octahedron  (111)  =  54°  44'  8". 

Cube  (100)  A  dodecahedron  (110)  =  45°  0'  0". 

Octahedron  (111)  A  dodecahedron  (110)  =  35°  15'  52". 


TETRAGONAL  SYSTEM 


31 


VI.   TETRAGONAL   SYSTEM. 

Crystallographic  Axes.  The  crystallographic  axes  of  the 
Tetragonal  System  are  three  in  number  and  make  right  angles 
with  each  other.  The  two  horizontal  axes  are  equal  in  length 
and  interchangeable,  but  the  vertical  axis  is  of  some  different 
length  which  varies  with  each  tetragonal  mineral.  Fig.  76 
represents  the  crystallographic  axes 
for  the  tetragonal  mineral  zircon. 
The  length  of  the  horizontal  axes  ~a» 

is  taken  as  unity,  and  the  relative 
length  of  the  vertical  axis  is  expressed 
in  terms  of  the  horizontal.  This 
length  has  to  be  determined  for  each 
tetragonal  mineral  by  measuring  the 


-c 
Fig.  76.    Tetragonal  Axes. 


interfacial  angles  on  a  crystal  and  making  the  proper  calcu- 
lations. For  zircon  the  length  of  the  vertical  axis  is  expressed 
as  c  =  0.640.  The  proper  orientation  of  the  crystallographic 
axes  and  the  method  of  their  notation  is  like  that  of  the  Iso- 
metric System  and  is  shown  in  Fig.  76. 

Normal  Class. 

Symmetry  and  Forms.  The  symmetry  of  the  Normal  Class 
of  the  Tetragonal  System  is  as  follows:  The  vertical  crystal- 
lographic axis  is  an  axis  of  tetragonal  symmetry.  There  are 


Fig.  77.  Fig.  78. 

Symmetry  of  Normal  Class,  Tetragonal  System. 

four  horizontal  axes  of  binary  symmetry,  two  of  which  are  coin- 
cident with  the  crystallographic  axes,  while  the  other  two  bisect 
the  angles  between  these.  Fig.  77  shows  the  axes  of  symmetry. 


32 


MANUAL  OF  MINERALOGY 


There  are  four  vertical  and  one  horizontal  planes  of  symmetry. 
Each  vertical  plane  of  symmetry  passes  through  one  of  the 
horizontal  axes  of  symmetry.  The  position  of  the  planes  of 
symmetry  is  shown  in  Fig.  78. 

The  forms  of  the  Normal  Class,  Tetragonal  System,  are  as 
follows : 

1.  Prism  of  First  Order.  The  prism  of  the  first  order  consists 
of  four  rectangular  vertical  faces,  each  of  which  intersects  the 
two  horizontal  crystallographic  axes  equally.  Its  symbol  is  (110). 
The  form  is  represented  in  Fig.  79. 

001  ^ 001 


^" 

H^P^ 
j  i 

i 

^ 

<4-, 

1 

^~ 

m 

!  m 

a  J 

a 

i 

..__ 

4i~ 

j  ^ 

110 

1! 

loo  i 

010 

210 

^10 

120 

-210 

| 

1 

1 

1   i 

"^^LT" 

.^_t"-~ 

^^ 

_--~- 

-4--L. 

--- 

Fig.  79.                               Fig.  80. 

Fig.  81. 

irst  Order  Prism.           Second  Order  Prism.            Ditetragonal  Prism. 

2.  Prism  of  Second  Order.    The  prism  of  the  second  order 
consists  of  four  rectangular  vertical  faces,  each  of  which  inter- 
sects one  horizontal  crystallographic  axis  and  is  parallel  to  the 
other  two  axes.    Its  symbol  is  (100).     The  form  is  represented 
in  Fig.  80. 

3.  Ditetragonal  Prism.    The  ditetragonal  prism  is  a  form  con- 
sisting of  eight  rectangular  vertical  faces,  each  of  which  inter- 
sects the  two  horizontal  crystallographic  axes  unequally.     There 
are  various  ditetragonal  prisms,  depending  upon  their  differing 
relations  to  the  horizontal  axes.    The  symbol  of  a  common 
form  is  (210),  which  is  represented  in  Fig.  81. 

4.  Pyramid  of  First  Order.    The  pyramid  of  the  first  order  is  a 
form  consisting  of  eight  isosceles  triangular  faces,  each  of  which 
intersects  all  three  crystallographic  axes,  the  intercepts  upon 
the  two  horizontal  axes  being  equal.    There  are  various  pyramids 


TETRAGONAL  SYSTEM 


33 


of  the  first  order,  depending  upon  the  inclination  of  their  faces. 
The  unit  pyramid  which  intersects  all  the  axes  at  their  unit 
lengths  is  the  most  common,  its  symbol  being  (111).  Symbols 
for  other  pyramids  of  the  first  order  are  (221),  (331),  (112), 
(113),  etc.  Fig.  82  represents  the  unit  pyramid  on  zircon. 

5.  Pyramid  of  Second  Order.  The  pyramid  of  the  second 
order  is  a  form  composed  of  eight  isosceles  triangular  faces,  each 
of  which  intersects  one  horizontal  axis  and  the  vertical  axis  and 
is  parallel  to  the  second  horizontal  axis.  There  are  various  pyra- 
mids of  the  second  order,  with  different  intersections  upon  the 
vertical  axis.  The  most  common  form  is  the  unit  pyramid, 


Fig.  82. 
First  Order  Pyramid. 


Fig.  83. 
Second  Order  Pyramid. 


Fig.  84. 
Ditetragonal  Pyramid. 


which  has  (101)  for  its  symbol.  Other  pyramids  of  the  second 
order  would  have  the  symbols  (201),  (301),  (102),  (103),  etc. 
Fig.  83  represents  a  unit  pyramid  of  the  second  order  upon 
zircon. 

6.  Ditetragonal  Pyramid.  The  ditetragonal  pyramid  is  a  form 
composed  of  sixteen  isosceles  triangular  faces,  each  of  which  in- 
tersects all  three  of  the  crystallographic  axes,  cutting  the  two 
horizontal  axes  at  different  lengths.  There  are  various  ditet- 
ragonal pyramids,  depending  upon  the  different  axial  intersec- 
tions possible.  One  of  the  most  common  is  the  pyramid  having 
(311)  for  its  symbol.  This  is  shown  as  it  would  appear  upon 
zircon  in  Fig.  84. 


34 


MANUAL  OF  MINERALOGY 


7.  Basal  Pinacoid.  The  basal  pinacoid,  basal  plane,  or  base, 
as  it  is  variously  called,  is  a  form  composed  of  two  horizontal 
faces.  Its  symbol  is  (001).  It  is  shown  in  combination  with  a 
prism  in  Figs.  79,  80  and  81. 


Fig.  85.    Zircon. 


Fig.  86.    Zircon.       Fig.  87.    Zircon.      Fig.  88'.   Zircon. 


Fig.  89.    Vesuvianite.       Fig.  90.    Vesuvianite. 


Fig.  91.    Rutile. 


Fig.  92.    Cassiterite.         Fig.  93.    Apophyllite.       Fig.  94.    Apophyllite. 

Tetragonal  Combinations.  The  different  pyramids  are  the 
only  tetragonal  forms  that  can  occur  alone,  and  even  they  are 
ordinarily  found  in  combination  with  other  forms.  Character- 
istic combinations  are  represented  in  Figs.  85-94. 


TETRAGONAL  SYSTEM 


35 


Sphenoidal  Class. 

The  Sphenoidal  Class  corresponds  in  the  Tetragonal  System 
to  the  Tetrahedral  Class  in  the  Isometric  System.  It  is  charac- 
terized by  the  following  symmetry:  The  three  crystallographic 
axes  are  axes  of  binary  symmetry  (see  Fig.  95),  and  there  are  two 
vertical  diagonal  planes  of  symmetry  (see  Fig.  96). 

2, 


Fig.  95.  Fig.  96. 

Symmetry  of  Sphenoidal  Class,  Tetragonal  System. 

Sphenoid.  The  characteristic  form  of  the  class  is  known  as 
a  sphenoid  (from  a  Greek  word  meaning  axlike):  It  consists  of 
four  isosceles  triangular  faces  which  intersect  all  three  of  the 
crystallographic  axes,  the  intercepts  on  the  two  horizontal  axes 
being  equal.  The  faces  correspond  in  their  position  to  the  alter- 


Fig.  97. 
Sphenoid. 


Fig.  98. 
Sphenoid. 


Fig.  99. 
Positive  and  Negative  Sphenoids. 


nating  faces  of  the  tetragonal  pyramid  of  the  first  order.  There 
may  be  different  sphenoids,  depending  upon  their  varying  inter- 
sections with  the  vertical  axes.  Two  different  sphenoids  are 
shown  in  Figs.  97  and  98.  There  may  also  be  a  positive  and  a 
negative  sphenoid,  the  combination  of  the  two  being  represented 
in  Fig.  99. 


MANUAL  OF  MINERALOGY 


The  sphenoid  differs  from  the  tetrahedron  in  the  fact  that  its 
vertical  crystallographic  axis  is  not  of  the  same  length  as  the 
horizontal  axes.  The  only  common  sphenoidal  mineral  is  chal- 
copyrite.  The  length  of  the  vertical  axis  in  chalcopyrite  is  very 
close  to  that  of  the  horizontal  axes,  c  =  0.985.  In  the  case  of 
the  unit  sphenoid,  therefore,  it  would  require  accurate  measure- 
ments in  order  to  differentiate  it  from  an  isometric  tetrahedron. 
Chalcopyrite  crystals  ordinarily  show  only  the  unit  sphenoid 
(Fig.  98),  but  at  times  show  a  steeper  sphenoid  (Fig.  97). 


Tri-Pyramidal  Class. 

Another  division  of  lower  symmetry  of  the  Tetragonal  System 
is  known  as  the  Tri-pyramidal  Class.  It  is  characterized  by  a 
form  known  as  the  pyramid  of  the  third  order. 
This  form  consists  of  eight  faces  which  correspond 
in  their  position  to  one-half  of  the  faces  of  a  di- 
tetragonal  pyramid.  The  minerals  found  in  this 
class  are  few  and  rare.  Moreover,  their  crystals 
seldom  show  the  faces  of  the  pyramid  of  the  third 
order,  and  when  these  do  occur  they  are  usually 
quite  small.  Therefore  it  seems  hardly  necessary 
in  this  place  to  consider  this  class  in  greater  detail. 
Fig.  100  is  of  a  crystal  of  scapolite,  upon  which  the 
faces  of  the  third-order  pyramid  z  are  shown. 


Fig.  100. 
Scapolite. 


Characteristics  of  Tetragonal  Crystals. 

Since  the  only  common  tetragonal  mineral  that  does  not  be- 
long to  the  Normal  Class  is  chalcopyrite,  which,  moreover,  is  to 
be  easily  recognized  by  its  general  physical  characteristics,  we 
may  confine  ourselves  here  to  the  consideration  only  of  the 
crystals  of  the  Normal  Class. 

The  striking  characteristics  of  tetragonal  crystals  may  be 
summarized  as  follows:  One  axis  of  tetragonal  symmetry;  the 
length  of  the  crystal  parallel  to  this  axis  is  usually  greater  or  less 
than  its  other  dimensions;  the  cross  section  of  a  crystal  when 
viewed  in  the  direction  of  the  axis  of  tetragonal  symmetry  con- 
sists usually  of  a  square  or  a  truncated  square. 


HEXAGONAL  SYSTEM 


37 


VII.   HEXAGONAL   SYSTEM. 

Crystallographic  Axes.  The  crystallographic  axes  of  the 
hexagonal  system  are  four  in  number.  Three  of  these  lie  in  the 
horizontal  plane,  while  the  fourth  is  vertical.  The  three  hori- 
zontal axes  are  of  equal  length  and  interchangeable.  They 
make  angles  of  60°  and  120°  with  each  other.  The  vertical  axis 
varies  in  its  relative  length  for  each  hexagonal  mineral,  and  this 
is  expressed  in  terms  of  the  length  of  the  horizontal  axes,  which 
is  taken  as  unity.  Thus  in  the  case  of  beryl,  the  vertical  axis, 
designated  as  c,  has  a  length  which  in  relation  to  the  length  of 
the  horizontal  axes  can  be  expressed  as  c  =  0.499. 


-a2 


+a2 


-as 


Fig.  101. 


-a3 


-c 

Fig.  102. 


Hexagonal  Axes. 


When  properly  orientated,  one  of  the  horizontal  crystallo- 
graphic axes  is  parallel  to  the  observer,  and  the  other  two  make 
30°  angles  on  either  side  of  a  line  perpendicular  to  him.  Fig. 
101  shows  the  proper  position  of  the  horizontal  axes  when 
viewed  in  the  direction  of  the  vertical  axis.  As  the  three  hori- 
zontal axes  are  interchangeable  with  each  other,  they  are  usually 
designated  ah  a*  and  a3.  Note  that  ai  is  to  the  left  of  the  observer 
with  its  positive  end  at  the  front,  that  o2  is  parallel  to  the  ob- 
server and  its  positive  end  is  at  the  right,  while  a3  is  to  the  right 
of  the  observer  and  its  positive  end  is  at  the  back.  Fig.  102 
shows  the  four  axes  in  clinographic  projection.  In  giving  the 
indices  of  any  face  upon  a  hexagonal  crystal  four  numbers  must 


38 


MANUAL  OF  MINERALOGY 


be  given,  since  there  are  four  axes.  The  numbers  referring 
to  the  intercepts  of  the  face  with  the  three  horizontal  axes  are 
given  first  in  their  proper  order,  while  the  number  referring  to 
the  intercept  on  the  vertical  axis  is  given  last. 

Normal  Class. 

Symmetry  and  Forms.  The  symmetry  of  the  Normal  Class 
of  the  Hexagonal  System  is  as  follows:  The  vertical  crystallo- 
graphic  axis  is  an  axis  of  hexagonal  symmetry.  There  are  six 
horizontal  axes  of  binary  symmetry,  three  of  them  being  coin- 
cident with  the  crystallographic  axes  and  the  other  three  lying 
midway  between  them  (see  Fig.  103).  There  is  a  horizontal 


Fig.  103.  Fig.  104. 

Symmetry  of  Normal  Class,  Hexagonal  System. 

plane  of  symmetry  and  six  vertical  planes  of  symmetry  (see 
Fig.  104).    The  forms  of  the  Normal  Class  are  as  follows: 

1.  Prism  of  First  Order.    This  is  a  form  consisting  of  six 
rectangular  vertical  faces  each  of  which  intersects  two  of  the 
horizontal  crystallographic  axes  equally  and  is  parallel  to  the 
third.    Fig.  105  shows  the  prism  of  the  first  order.    The  symbol 
for  the  form  is  (1010). 

2.  Prism  of  Second  Order.    This  is  a  form  consisting  of  six 
rectangular  vertical  faces,  each  of  which  intersects  two  of  the 
horizontal  axes  equally  and  the  intermediate  horizontal  axis  at 
one-half  this  distance.    Fig.  106  shows  the  prism  of  the  second 
order.    The  symbol  for  the  form  is  (1120). 


HEXAGONAL  SYSTEM 


89 


3.  Dihexagonal  Prism.    The  dihexagonal  prism  has  twelve  rec- 
tangular vertical  faces,  each  of  which  intersects  all  three  of  the 


^~— 

oc 

101  C 

~NS, 

_-t  — 

1100 

10 

to 

ofio 

m 

u 

r 

1 

i 

I 
1 

I 

\ 

_  —  -* 

2110 


1120 


Fig.  105. 
Prism  of  First  Order. 


Fig.  106. 
Prism  of  Second  Order. 


Fig.  107. 
Dihexagonal  Prism. 


horizontal  crystallographic  axes  at  different  lengths.  There  are 
various  dihexagonal  prisms,  depending  upon  their  differing  rela- 
tions to  the  horizontal  axes.  The  symbol  of  a  common  dihexago- 
nal prism  is  (2130)  (see  Fig.  107). 


Fig.  108.  Fig.  109.  Fig.  110. 

Pyramid  of  First  Order.     Pyramid  of  Second  Order.      Dihexagonal  Pyramid. 

4.  Pyramid  of  First  Order.  This  form  consists  of  twelve 
isosceles  triangular  faces,  each  of  which  intersects  two  of  the 
horizontal  crystallographic  axes  equally,  is  parallel  to  the  third 
horizontal  axis  and  intersects  the  vertical  axis  (see  Fig.  108). 
There  are  various  pyramids  of  the  first  order  possible,  depending 
upon  the  inclination  of  their  faces.  The  unit  form  would  have 
the  symbol  (lOTl). 


40 


MANUAL  OF  MINERALOGY 


5.  Pyramid  of  the  Second  Order.    This  is  a  form  composed  of 
twelve  isosceles  triangular  faces,  each  of  which  intersects  two  of 
the  horizontal  axes  equally,  the  third  and  intermediate  horizon- 
tal axis  at  one-half  this  distance,  and  also  intersects  the  vertical 
axis  (see  Fig.  109).    There  are  various  pyramids  of  the  second 
order  possible,  depending  upon  the  inclination  of  their  faces.    A 
common  form  would  have  for  its  symbol  (1122). 

6.  Dihexagonal  Pyramid.     The  dihexagonal  pyramid  is  a  form 
of  twenty-four  isosceles  triangular  faces,  each  of  which  intersects 
all  three  of  the  horizontal  axes  differently  and  intersects  also  the 
vertical  axis.    This  form  is  shown  in  Fig.  110.    There  are  differ- 
ent dihexagonal  pyramids  which  vary  in  their  intercepts,  one  of 
the  most  common  having  for  its  symbol  (2131). 

7.  Basal  Pinacoid.    The  basal  pinacoid  is  a  form  composed 
of  two  horizontal  faces.     It  is  shown  in  combination  with  the 
different  prisms  in  Figs.  105,  106  and  107.    Its  symbol  is  (0001). 

?r^= 

Yn\n 


11 


Fig.  111. 


Fig.  112.  Fig.  113. 

Beryl  Crystals. 


Fig.  114. 


Figs.  111-114  show  various  combinations  of  the  forms  of  this 
class. 

Tri-Pyramidal  Class. 

A  division  of  the  Hexagonal  System  showing  lower  symmetry 
than  that  of  the  Normal  Class  is  known  as  the  Tri-pyramidal 
Class.  It  has  a  vertical  axis  of  hexagonal  symmetry  and  a 
horizontal  plane  of  symmetry.  It  is  characterized  by  the  form 
known  as  the  pyramid  of  the  third  order.  This  form  consists 
of  twelve  faces,  which  correspond  in  their  position  to  one-half 
of  the  faces  of  a  dihexagonal  pyramid.  The  minerals  of  the 


HEXAGONAL  SYSTEM 


41 


Apatite  Group  are  the  only  ones  of  importance  in  this  class,  and 
upon  their  crystals  the  pyramid  of  the  third  order  is  rarely  to  be 
seen.  When  it  is  observed  it  shows  usually  only  small  faces. 
Fig.  115  represents  a  complex  crystal  of  apatite  with  the  faces 
of  a  third-order  pyramid  (AI)  upon  it. 


Fig.  115.    Apatite. 


Fig.  116.    Zincite. 


Hemimorphic  Class. 

The  crystals  of  certain  rare  minerals  show  the  forms  of  the 
Normal  Class  but  with  hemimorphic  development.  A  hemi- 
morphic  crystal  is  one  that  shows  different  forms  or  combinations 
of  forms  at  the  opposite  ends  of  a  symmetry  axis.  Fig.  116 
represents  a  crystal  of  zincite  with  a  prism  terminated  by  a 
pyramid  above  and  a  basal  pinacoid  below. 

Rhombohedral  Class.    Normal  Division. 

The  forms  of  this  class  are  to  be  referred  to  the  hexagonal 
crystallographic  axes,  but  show  a  lower  symmetry  than  those  of 
the  Normal  Class. 
8J 


Fig.  117.  Fig.  118. 

Symmetry  of  Rhombohedral  Class,  Hexagonal  System. 

Symmetry  and  Forms.    The  vertical  crystallographic  axis 
is  one  of  trigonal  symmetry,  and  the  three  horizontal  crystallo- 


42 


MANUAL  OF  MINERALOGY 


graphic  axes  are  axes  of  binary  symmetry  (see  Fig.  117).  There 
are  three  vertical  planes  of  symmetry  bisecting  the  angles  be- 
tween the  horizontal  axes  (see  Fig. 
118). 

1.  Rhomhohedron.  The  rhombohe- 
dron  is  a  form  consisting  of  six  rhom- 
bic-shaped faces,  which  correspond  in 
their  position  to  the  alternate  faces  of 
a  hexagonal  pyramid  of  the  first  order. 
The  relation  of  these  two  forms  to  each 
other  is  shown  in  Fig.  119.  There  may 

Fig.  119.    Showing  Relation  be-    . 

tween  First  Order  Pyramid  be  two  different   orientations  of  the 
rhombohedron.     A   positive  rhombo- 

hedron  is  shown  in  Fig.  120  and  a  negative  rhombohedron  in 
Fig.  121.    It  is  to  be  noted  that  when  properly  orientated  the 


Fig.  120.    Positive  Rhombohedron.         Fig.  121.     Negative  Rhombohedron. 

positive  rhombohedron  has  one  of  its  faces,  and  the  negative 
rhombohedron  one  of  its  edges,  toward  the  observer.  There 
are  various  rhombohedrons,  which  differ  from  each  other  in 
the  inclination  of  their  faces.  The  symbol  of  the  unit  positive 
rhombohedron  is  (lOll)  and  of  the  unit  negative  rhombohedron 
(0111).  Characteristic  combinations  of  positive  and  negative 
rhombohedrons  with  each  other  and  with  other  hexagonal  forms 
are  shown  in  Figs.  122-130. 

2.  Scalenohedron.  This  form  consists  of  twelve  scalene  tri- 
angular faces.  These  faces  correspond  hi  their  position  to  the 
alternate  pairs  of  faces  of  a  dihexagonal  pyramid.  The  relation 
of  the  two  forms  to  each  other  is  shown  in  Fig.  131.  The  striking 
characteristics  of  the  scalenohedron  are  the  zigzag  middle  edges 


HEXAGONAL  SYSTEM 


43 


Fig.  122.  Caloite.        Fig.  123.  Caloite.     Fig.  124.  Calcite. 


Fig.  126.  Calcite.       Fig.  127.  Calcite. 


Fig.  128.    Chabazite.  Fig.  129.    Corundum.          Fig.  130.    Corundum, 


Fig.  131.    Showing  Relation  between  Dihex-         Fig.  132.    Scalenohedron. 
agonal  Pyramid  and  Scalenohedron. 


44 


MANUAL  OF  MINERALOGY 


Fig.  133.    Calcite. 


Fig.  134.    Calcite. 


Fig.  135.    Calcite.  Fig.  136.    Calcite.  Fig.  137.    Tourmaline. 


Fig.  138.    Tourmaline.  Fig.  139.    Tourmaline.      Fig.  140     Tourmaline 


HEXAGONAL  SYSTEM  45 

which  differentiate  it  from  an  ordinary  pyramid  and  the  alter- 
nating, relatively  obtuse  and  acute  angles  over  the  edges  that 
meet  at  the  vertices  of  the  form.  There  are  many  different 
possible  scalenohedrons,  depending  upon  the  varying  slope  of 
their  faces.  A  common  scalenohedron  having  the  symbol  (2131) 
is  represented  in  Fig.  132.  Characteristic  combinations  of  sca- 
lenohedrons with  other  forms  are  shown  in  Figs.  133-136. 

Rhombohedral  Class.     Hemimorphic  Division. 

Tourmaline  crystals  show  the  forms  of  the  Rhombohedral 
Class  but  with  hemimorphic  development.  They  are  also  com- 
monly characterized  by  the  presence  of  three  faces  of  a  triangular 
prism.  Figs.  137-140  represent  characteristic  hemimorphic  tour- 
maline crystals. 

Rhombohedral  Class.     Tri-Rhombohedral  Division. 

This  is  a  subdivision  of  the  Rhombohedral  Class,  which  con- 
tains only  a  few  and  rare  minerals.  It  is  characterized  by  the 
forms  known  as  the  rhombohedrons  of  the  second  and  third 
orders.  The  faces  of  a  second-order  rhombohedron  correspond 
in  position  to  one-half  the  faces  of  the  second-order  hexagonal 
pyramid,  and  those  of  the  third  order  to  one-quarter  of  the  faces 
of  the  dihexagonal  pyramid. 

Rhombohedral  Class.     Trapezohedral  Division. 

The  only  important  mineral  of  this  class  that  is  commonly 
found  in  crystals  is  quartz,  and  its  crystals  as  a  rule  do  not  show 
forms  other  than  those  of  the  Rhombohedral  Class,  Normal 
Division.  At  times,  however,  small  faces  may  occur  of  a  form 
known  as  a  trapezohedron,  which  shows  a  lower  symmetry.  This 
form  has  six  faces,  which  correspond  in  their  position  to  one-quar- 
ter of  the  faces  of  a  dihexagonal  pyramid.  The  quartz  crystals 
are  said  to  be  right-  or  left-handed,  depending  upon  whether  these 
faces  are  to  be  observed  truncating  the  edges  between  prism  and 
rhombohedron  faces  at  the  right  or  at  the  left.  Figs.  141  and 
142  represent  these  two  types. 


MANUAL  OF  MINERALOGY 


Fig.  141. 
Right-handed  Quartz. 


Fig.  142. 
Left-handed  Quartz. 


Characteristics  of  Hexagonal  Crystals. 

Hexagonal  crystals  are  most  readily  recognized  by  the  follow- 
ing facts:  The  vertical  crystallographic  axis  is  one  of  either 
hexagonal  or  trigonal  symmetry.  The  crystals  are  commonly 
prismatic  in  habit.  When  viewed  in  the  direction  of  the  vertical 
axis,  they  usually  show  a  hexagonal  cross  section. 

VIII.   ORTHORHOMBIC   SYSTEM. 

Crystallographic  Axes.  The  crystallographic  axes  of  the 
orthorhombic  system  are  three  in  number.  They  make  90° 
angles  with  each  other  and  are  of  unequal  lengths.  The  rela- 
te 


—o 

Fig.  143. 
Orthorhombic  Axes. 


1 

~12'^~~~-~~-~^ 

| 

i* 

*» 

H     $ 
i. 

^--^^ 

Fig.  144. 
Axes  of  Symmetry. 
Drthorhombic  System 

Fig.  145. 

Planes  of  Symmetry. 
Orthorhombic  System, 


ORTHORHOMBIC  SYSTEM 


47 


tive  lengths  of  the  axes,  or  the  axial  ratio,  has  to  be  deter- 
mined for  each  orthorhombic  mineral.  Any  one  of  the  three 
axes  may  be  chosen  as  the  vertical  or  c  axis.  The  longer  of  the 
other  two  is  taken  as  the  b  axis  and  is  called  the  macro-axis. 
The  shorter  of  the  horizontal  axes  is  taken  as  the  a  axis  and  is 
called  the  br achy-axis.  The  length  of  the  b  axis  is  taken  as  unity 
and  the  relative  lengths  of  the  a  and  c  axes  are  given  in  terms 
of  it.  Fig.  143  represents  the  crystallographic  axes  for  the 
orthorhombic  mineral  sulphur,  whose  axial  ratio  would  be  as 
follows:  a  :  b  :  c  =  0.813  :  1  :  1.903. 

Normal  Class. 

Symmetry  and  Forms.  The  symmetry  of  the  Normal  Class, 
Orthorhombic  System,  is  as  follows :  The  three  crystallographic 
axes  are  axes  of  binary  symmetry  and  the  three  axial  planes  are 
planes  of  symmetry  (see  Figs.  144  and  145). 

1.  Pyramid.  An  orthorhombic  pyramid  has  eight  triangular 
faces,  each  of  which  intersects  all  three  of  the  crystallographic 
axes.  There  are  various  different  pyramids  with  varying  inter- 
cepts on  the  axes.  A  unit  pyramid  (see  Fig.  146)  would  have 
for  its  symbol  (111). 


no 


no 


Fig.  146.    Pyramid. 


Fig.  147.    Priam  and  Base. 


2.  Prism.  An  orthorhombic  prism  has  four  vertical  rectan- 
gular faces,  each  of  which  intersects  the  two  horizontal  axes. 
There  are  various  prisms,  depending  upon  their  differing  rela- 
tions to  the  horizontal  axes.  A  unit  prism  (see  Fig.  147)  would 
have  for  its  symbol  (110). 


48 


MANUAL  OF  MINERALOGY 


3.  Macrodome.  A  macrodome  is  a  form  consisting  of  four 
rectangular  faces,  each  of  which  intersects  the  a  and  c  axes  and 
is  parallel  to  the  b  or  macro-axis.  It  is  named  from  the  axis  to 
which  it  is  parallel.  There  are  various  macrodomes  with  differ- 
ent axial  intercepts.  A  unit  form  (see  Fig.  148)  would  have 
for  its  symbol  (101). 


Fig.  148. 
Macrodome  and  Brachypinacoid. 


Oil 


Oil 


Fig.  149. 
Brachydome  and  Macropinacoid. 


)0] 


4.  Brachydome.    The  brachydome  consists  of  four  rectangular 
faces,  each  of  which  intersects  the  b  and  c  axes  and  is  parallel 
to  the  a  or  brachy-axis.     There  are  various  brachydomes  with 
different  axial  intercepts.    A  unit  form   (see  Fig.   149)  would 
have  for  its  symbol  (Oil). 

5.  Macropinacoid.    The  macropinacoid  has  two  parallel  faces, 
each  of  which  intersects  the  a  axis  and  is  parallel  to  the  b  and  c 

axes.  It  derives  its  name  from  the 
fact  that  it  is  parallel  to  the  b  or 
macro-axis.  It  is  represented  in  Fig. 
150  and  its  symbol  is  (100). 

6.  Brachypinacoid.  This  is  a  form 
consisting  of  two  parallel  faces,  each 
of  which  intersects  the  b  axis  and  is 
parallel  to  the  a  (brachy)  and  the  c 
axes.  It  is  represented  in  Fig.  150 
and  its  symbol  is  (010). 
7.  Basal  Pinacoid.  The  basal  pinacoid  is  a  form  consisting 

of  two  horizontal  faces.     It  is  represented  in  Fig.  150  and  its 

symbol  is  (001). 


010 


Fig.  150. 

Macropinacoid,  Brachypinacoid, 
and  Basal  Pinacoid. 


ORTHORHOMBIC  SYSTEM 


49 


m 


Fig.  151.    Sulphur.  Fig.  152.    Sulphur.  Fig.  153.    Staurolite. 


Fig.  157.    Brookite. 


Fig.  158.    Anglesite. 


Fig.  159.    Barite. 


Fig.  160.    Barite. 


Fig.  161.    Celeatite. 


50  MANUAL  OF  MINERALOGY 

Combinations.      Practically  all  orthorhombic  crystals  consist 
of  combinations  of  two  or  more  forms.     Characteristic  com- 
binations of  the  various  forms  are  given  in  Figs. 
151-161. 

Hemimorphic  Class. 

The  only  orthorhombic  mineral  of  importance 
belonging  to  this   class   is   calamine.     When  its 
crystals  are  doubly  terminated  they   show   dif- 
erent  forms  at  either   end  of  the  vertical  axis. 
Fig.  162.       pig.  162  represents  a  characteristic  crystal. 

Calamine. 

Characteristics  of  Orthorhombic  Crystals. 

The  most  distinguishing  characteristics  of  orthorhombic  crys- 
tals are  as  follows:  The  three  chief  directions  at  right  angles 
to  each  other  are  of  different  lengths.  These  three  directions 
are  axes  of  binary  symmetry.  The  crystals  are  commonly  pris- 
matic in  their  development  and  show  usually  cross  sections  that 
are  either  rectangles  or  truncated  rectangles. 


IX.   MONOCLINIC   SYSTEM. 

Crystallographic  Axes.  The  crystallographic  axes  of  the 
Monoclinic  System  are  three  in  number.  They  are  of  unequal 
lengths.  The  axes  a  and  b,  and  6  and  c,  make  90°  angles  with 
each  other,  but  a  and  c  make  some  oblique  angle  with  each 
other.  The  relative  lengths  of  the  axes  and  the  angle  between 
the  a  and  c  axes  vary  for  each  monoclinic  mineral  and  have  to  be 
determined  in  each  case  from  appropriate  measurements.  The 
a  axis  is  known  as  the  dino-axis,  while  the  b  axis  is  known  as 
the  ortho-axis.  The  length  of  the  b  axis  is  taken  as  unity  and  the 
lengths  of  the  a  and  c  axes  are  expressed  in  terms  of  it.  When 
properly  orientated  the  c  axis  is  vertical,  the  b  axis  is  horizontal 
and  parallel  to  the  observer,  and  the  a  axis  is  inclined  down- 
ward toward  him.  The  smaller  of  the  two  supplementary 
angles  that  a  and  c  make  with  each  other  is  designated  as  /?. 


MONOCLINIC  SYSTEM 


51 


Fig.  163  represents  the  crystallographic  axes  of  the  monoclinic 
mineral  orthoclase,  the  axial  constants  of  which  are  expressed 
as  follows:  a  :  b  :  c  =  0.658;  1  :  0.555;  ft  =  63°  57'. 


— 


Fig.  163.     Monoclinic  Axes. 

Normal  Class. 

Symmetry  and  Forms.  The  symmetry  of  the  Normal  Class 
of  the  Monoclinic  System  is  as  follows:  The  crystallographic 
axis  b  is  an  axis  of  binary  symmetry  and  the  plane  of  the  a  and 


Fig.  164.  Fig.  165. 

Symmetry  of  Monoclinic  System. 


The 


c  axes  is  a  plane  of  symmetry  (see  Figs.  164  and  165). 
forms  are  as  follows: 

1.  Pyramid.  A  monoclinic  pyramid  is  a  form  consisting  of 
four  triangular  faces,  each  of  which  intersects  all  three  of  the 
crystallographic  axes.  There  are  different  pyramids,  depending 
upon  varying  axial  intercepts.  There  are,  further,  two  inde- 
pendent types  of  monoclinic  pyramids,  depending  upon  whether 
the  two  faces  on  the  upper  half  of  the  crystal  intersect  the 


52 


MANUAL  OF  MINERALOGY 


positive  or  the  negative  end  of  the  a  axis.  A  unit  pyramid  of 
the  first  of  these  types  is  shown  in  Fig.  166  and  has  for  its  symbol 
(111).  A  unit  pyramid  of  the  second  of  these  types  is  repre- 
sented in  Fig.  167  and  has  for  its  symbol  (111).  Fig.  168  shows 
these  two  types  in  combination  with  each  other.  It  should  be 
emphasized  that  a  monoclinic  pyramid  consists  of  only  four 
faces,  two  of  which  are  to  be  found  intersecting  the  upper  end 
of  the  c  axis  and  the  other  two  intersecting  its  lower  end.  The 
two  types  described  above  are  entirely  independent  of  each  other. 


Fig.  166. 


Fig.  167. 
Monoclinic  Pyramids. 


Fig.  168. 


2.  Prism.     The  monoclinic  prism  has  four  vertical  rectangular 
faces,  each  of  which  intersects  the  a  and  b  axes.     There  are 
various  prisms  with  different  axial  intercepts.     A  unit  prism  is 
represented  in  Fig.  169  and  has  for  its  symbol  (110). 

3.  Orthodome.     An  orthodome  consists  of  two  parallel  faces, 
each  of  which  intersects  the  a  and  c  axes  and  is  parallel  to  the  b 
or  ortho-axis.     Its  name  is  derived  from  that  of  the  axis  to  which 
it  is  parallel.    There  are  different  orthodomes  with  different 
axial  intercepts.     There  are  also  two  distinct  and  independent 
types  of  orthodomes,  depending  upon  whether  the  face  upon  the 
upper  end  of  the  crystal  intersects  the  positive  or  negative  end 
of  the  a  axis.    These  two  types  of  orthodomes  are  represented 
in  combination  in  Fig.  170,  but  it  should  be  emphasized  that  they 
are  entirely  independent  of  each  other.    The  symbol  of  the  unit 
orthodome  in  front  is  (101)  and  that  of  the  one  behind  is  (T01). 

4.  Clinodome.    The  clinodome  is  a  form  having  four  faces, 
each  of  which  intersects  the  b  and  c  axes  and  is  parallel  to  the  a 
or  clino-axis.    There  are  various  clinodomes  with  differing  axial 


MONOCLINIC  SYSTEM 


53 


intercepts.     A  unit  form  is  represented  in  Fig.  171  and  would 
have  for  its  symbol  (Oil). 

5.  Orthopinacoid.    The  orthopinacoid  has  two  parallel  faces, 
each  of  which  intersects  the  a  axis  and  is  parallel  to  the  b  and  c 
axes.     It  derives  its  name  from  the  fact  that  it  is  parallel  to  the 
b  or  ortho-axis.    It  is  represented  in  Fig.  171  and  its  symbol  is 
(100). 

6.  Clinopinacoid.    The  clinopinacoid  consists  of  two  parallel 
faces,  each  of  which  intersects  the  b  axis  and  is  parallel  to  the  a 
(clino)  and  the  c  axes.     It  is  represented  in  Fig.  170  and  its 
symbol  is  (010). 


Fig.  169. 
Prism  and  Base. 


Fig.  170. 
Orthodomes  and  Clinopinacoid. 


Fig.  171. 
Clinodome  and 
Orthopinacoid. 


7.  Basal  Pinacoid.  The  basal  pinacoid  is  a  form  consisting 
of  two  parallel  faces,  each  of  which  intersects  the  vertical  axis 
and  is  parallel  to  the  a  and  b  axes.  It  is  represented  in  Fig.  169 
and  its  symbol  is  (001). 

Monoclinic  Combinations.  Characteristic  combinations  of  the 
forms  described  above  are  given  in  Figs.  172-179. 

Characteristics  of  Monoclinic  Crystals. 

Monoclinic  crystals  are  to  be  distinguished  chiefly  by  their 
low  symmetry.  The  fact  that  they  possess  but  one  plane  of 
symmetry  and  one  axis  of  binary  symmetry  at  right  angles  to 
it  would  serve  to  differentiate  them  from  the  crystals  of  all 
other  systems  and  classes.  Usually  the  inclination  of  the  crystal 
faces  which  are  parallel  to  the  clino-axis  is  marked. 


54 


MANUAL  OF  MINERALOGY 


Fig.  172.  Fig.  173. 

Pyroxene. 


Fig.  176. 
Gypsum. 


Fig.  177. 


Fig.  174.  Fig.  175. 

Amphibole. 


Fig.  178. 
Orthoclase. 


Fig.  179. 


X.   TRICLINIC   SYSTEM. 


Crystallographic  Axes.  The  crystallographic  axes  of  the 
Triclinic  System  are  three  in  number.  They  are  of  unequal 
lengths  and  make  oblique  angles  with  each  other.  The  axial 
directions  for  each  triclinic  mineral  are  chosen  arbitrarily,  but  in 
such  a  way  as  to  yield  the  simplest  relations.  Any  one  of  them 
may  be  taken  as  c,  the  vertical  axis.  The  longer  of  the  other 
two  is  designated  as  the  b  or  macro-axis,  while  the  shorter  is 
called  a  or  the  brachy-axis.  The  relative  lengths  of  the  three 
axes  and  the  angles  which  they  make  with  each  other  have  to 
be  calculated  for  each  mineral  from  appropriate  measurements. 
The  angles  which  the  different  axes  make  with  each  other  are 


TRIG  LIN  1C  SYSTEM 


55 


designated  respectively  as  «,  ft  and  7  (see  Fig.  180).  For  ex- 
ample, the  crystal  constants  of  the  triclinic  mineral  axinite  are 
as  follows:  a  :  b  :  c  =  0.482  :  1  :  0.480;  a  =  82°  54';  ft  =  91°  52'; 
T  =  131°  32'. 

Normal  Class. 

Symmetry  and  Forms.  The  symmetry  of  the  Normal  Class 
of  the  Triclinic  System  consists  only  in  a  center  of  symmetry 
(see  Fig.  5,  page  8).  It  has  no  axes  or  planes  of  symmetry. 
All  forms  of  the  Triclinic  System  consist  of  two  similar  and  paral- 
lel faces.  In  this  respect  all  triclinic  forms  might  be  spoken  of 
as  pinacoids.  They  are,  however,  usually  designated  as  pyramids 
when  their  faces  intersect  all  three  axes,  as  prisms  or  domes 
when  they  intersect  two  axes  and  as  pinacoids  when  they  inter- 
sect but  one  axis. 


Fig.  180. 
Triclinic  Axes. 


Fig.  181. 
Pyramids. 


Fig.  182. 
Prisms  and  Basal  Pinacoid. 


1.  Pyramid.    A   triclinic   pyramid  consists   of  two  parallel 
faces,  each  of  which  intersects  all  three  crystallographic  axes. 
There  are  four  possible  types,  depending  upon  the  octants  in 
which  the  faces  lie.    Fig.  181  shows  a  combination  of  four  unit 
pyramids. 

2.  Prisms.    A  triclinic  prism  consists  of  two  parallel  faces, 
each  of  which  intersects  the  a  and  b  axes  and  is  parallel  to  the 
c  axis.    There  are  two  possible  types,  a  combination  of  which 
is  shown  in  Fig.  182. 

3.  Domes.    A  triclinic  dome  consists  of  two  similar  parallel 
faces,  each  of  which  intersects  the  c  axis  and  either  the  a  or  6 
axes  and  is  parallel  to  the  other.    They  are  spoken  of  as  either 
macro-  or  brachydomes,  depending  upon  the  axis  to  which  they 
are  parallel.    There  are  two  types  of  each.    Fig.  183  represents 


56 


MANUAL  OF  MINERALOGY 


a  combination  of  the  two  types  of  macrodome  and  Fig.  184 
combination  of  the  two  brachydomes. 


Fig.  183. 
Macrodomes  and 
Brachypinacoid. 


Fig.  184. 

Brachydomes  and 
Macropinacoid. 


Fig.  185. 

Macropinacoid,  Brachypin- 
acoid, and  Basal  Pinacoid. 


Fig.  186. 
Axinite. 


Fig.  187. 
Rhodonite. 


Fig.  188. 
Chalcanthite. 


4.  Pinacoids.  A  triclinic  pinacoid  is  a  form  consisting  of  two 
parallel  faces,  each  of  which  intersects  one  crystallographic  axis 
and  is  parallel  to  the  other  two.  They  are  designated  as  the 
macropinacoid  with  the  symbol  (100),  as  the  brachypinacoid 
with  the  symbol  (010),  and  as  the  basal  pinacoid  with  the  symbol 
(001).  A  combination  of  the  three  forms  is  shown  in  Fig.  185. 

Triclinic  Combinations.  Figs.  186-188  represent  characteristic 
triclinic  crystals. 

Characteristics  of  Triclinic  Crystals. 

There  are  only  a  few  triclinic  minerals  and  they  seldom  show 
distinct  and  well-developed  crystals.  When  such  crystals  do 
occur  they  are  to  be  recognized  by  the  fact  that  they  have  no 
plane  or  axis  of  symmetry  and  by  the  fact  that  each  form  consists 
of  only  two  similar  and  parallel  faces. 


II.   GENERAL    PHYSICAL    PROPERTIES 
OF  MINERALS. 

I.   STRUCTURE   OF   MINERALS. 

IF  by  the  phrase  "structure  of  minerals"  is  meant  their  internal 
or  molecular  structure,  all  minerals  may  be  included  in  one  of 
two  classes:  (1)  Crystalline;  (2)  Amorphous.  With  only  a  few 
exceptions,  minerals  are  crystalline  in  their  structure.  This  does 
not  signify,  however,  that  these  minerals  necessarily  occur  in 
distinct  crystals,  but  only  that  their  internal  structure  is  such 
that  they  may  under  favorable  circumstances  definitely  crystal- 
lize. The  few  mineral  species  that  are  classified  as  amorphous 
possess  no  regular  internal  structure  and  therefore  cannot  crys- 
tallize. 

Commonly,  however,  the  expression  "structure  of  minerals" 
refers  to  their  outward  shape  and  form.  Various  descriptive 
terms  are  used  in  this  connection  that  will  need  short  definitions. 

1.  When  a  mineral  consists  of  distinct  crystals  the  follow- 
ing terms  may  be  used: 

a.  Crystallized.    In  definite  crystals  (see  A,  pi.  II). 

b.  Acicular.    In  slender  needlelike  crystals. 

c.  Capillary.     In  hairlike  crystals. 

d.  Filiform.    In  threadlike  crystals. 

e.  Dendritic.     Arborescent,   in  slender  divergent    branches, 
somewhat  plantlike,  made  up  of  more  or  less  distinct  crystals. 

f.  Reticulated.    Latticelike  groups  of  slender  crystals. 

g.  Divergent  or  Radiated.      Radiating  crystal  groups  (see  C, 
pi.  II). 

h.  Drusy.  A  surface  is  drusy  when  covered  with  a  layer  of 
very  small  crystals. 

57 


58  MANUAL  OF  MINERALOGY 

2.  When  a  mineral  consists  of  columnar  individuals  the 
following  terms  may  be  used: 

a.  Columnar.     In  stout  columnlike  individuals. 

b.  Fibrous.     In   slender    columnar   individuals.     The   fibers 
may  be  parallel  or  radiated  (see  D,  pi.  II.) 

c.  Stellated.    When  the  radiating  individuals  form  starlike  or 
circular  groups. 

d.  Globular.    When  the  radiating  individuals  form  spherical 
or  hemispherical  groups. 

e.  Botryoidal.    When  the  globular  forms  are  in  groups.     The 
word  is  derived  from  the  Greek  for  a  "bunch  of  grapes"  (see 
B,  pi.  III). 

f.  Reniform  or  Mammillary.     When  a  mineral  is  in  broad 
rounded  masses  resembling  in  shape  either  a  kidney  or  mamma3 
(see  A,  pi.  III). 

3.  When  a  mineral  consists  of  scales  or  lamellae. 

a.  Foliated.    When  a  mineral  separates  easily  into  plates  or 
leaves. 

b.  Micaceous.    Similar  to  foliated  but  the  mineral  can  be  split 
into  exceedingly  thin  sheets,  as  in  the  micas. 

c.  Lamellar  or  tabular.    When  a  mineral  consists  of  flat  plate- 
like  individuals  superimposed  upon  and  adhering  to  each  other. 

d.  Plumose.    Consisting   of   fine   scales   with   divergent   or 
featherlike  structure. 

4.  When  a  mineral  consists  of  grains. 

Coarse  to  fine  granular.    When    a   mineral   consists   of   an 
aggregate  of  large  or  small  grains. 

5.  Miscellaneous. 

a.  Compact  —  Earthy.    A  uniform  aggregate  of  exceedingly 
minute  particles. 

b.  Stalactitic.    When  a  mineral  has  the  shape  of  cylinders  or 
cones  which  have  been  formed  by  deposition  from  mineral- 
bearing  waters  dripping  from  the  roof  of  some  cavity  (see  B, 
pi.  II). 

c.  Concentric.    Consisting  of  more  or  less  circular  layers  super- 
imposed  upon  one  another  about   a  common  center  (see  C, 
pi.  III). 


PLATE  II. 


A. 


D. 


A.  Crystallized  —  Quartz. 

B.  Stalactitic— Limonite. 


C.  Radiated  — Natrolite. 

D.  Fibrous — Serpentine. 


PLATE  III. 


A.    Mammillary  or  Reniform  —  Hematite.        B.    Botryoidal  —  Chalcedony, 
C.    Concentric  —  Malachite. 


CLEAVAGE,  PARTING  AND  FRACTURE     59 

d.  Banded.    When  a  mineral  occurs  in  narrow  parallel  bands 
of  different  color  or  texture. 

e.  Geodes.    When  a  cavity  has  been  lined  by  the  deposition 
of  mineral  material  but  not  wholly  filled,  the  more  or  less  spherical 
mineral  shell  is  called  a  geode.    The  mineral  is  often  banded 
owing  to  successive  depositions  of  the  material,  and  the  inner 
surface  is  frequently  covered  with  projecting  crystals. 

f .  Massive.    When  a  mineral  is  composed  of  compact  material 
with  an  irregular  form  and  does  not  show  any  peculiar  structure 
like  those  described  above,  it  is  said  to  be  massive. 

II.   CLEAVAGE,  PARTING  AND  FRACTURE. 

1.  Cleavage.     If  a  mineral,  when  the  proper  force  is  applied, 
breaks  so  that  it  shows  definite  plane  surfaces,  it  is  said  to  possess 
a  cleavage.    These  cleavage  surfaces  resemble  natural  crystal 
faces.    They  are  always  parallel  to  some  possible  crystal  face, 
and  usually  to  one  having  simple  relations  to  the  crystallographic 
axes.    They  may  be  perfect,  as  in  the  cases  of  the  micas,  calcite, 
gypsum,  etc.,  or  they  may  be  more  or  less  obscure.     Cleavage  is 
due  to  the  fact  that  in  the  mineral 

structure  there  is  a  certain  plane  or 
planes  along  which  the  molecular  co- 
hesion is  weaker  than  in  other  direc- 
tions. All  minerals  do  not  show 
cleavage,  and  only  a  comparatively 
few  show  it  in  an  eminent  degree. 
The  quality  of  the  cleavage  and  its 
crystallographic  direction  are  often 
important  aids  in  the  identification  of  Fie-  189-  Cubic  Cleavage  - 
a  mineral.  The  cleavage  of  a  mineral 

is  described  according  to  the  crystal  face  to  which  it  is  parallel, 
as  cubic  cleavage  (galena,  halite)  (see  Fig.  189),  octahedral 
cleavage  (fluorite),  dodecahedral  cleavage  (sphalerite),  rhombo- 
hedral  cleavage  (calcite),  prismatic  cleavage  (amphibole),  basal 
cleavage  (topaz),  pinacoidal  cleavage  (stibnite),  etc. 

2.  Parting.     Certain  minerals  when  subjected  to  a  strain  or 
pressure  develop  planes  of  molecular  weakness  along  which  they 


60  MANUAL  OF  MINERALOGY 

may  subsequently  be  broken.  When  plane  surfaces  are  produced 
on  a  mineral  in  this  way  it  is  said  to  have  a  parting.  This 
phenomenon  resembles  cleavage,  but  is  to  be  distinguished  from 
it  by  the  facts  that  not  every  specimen  of  a  certain  mineral  will 
exhibit  it,  but  only  those  specimens  which  have  been  subjected 
to  the  proper  pressure,  and  that  even  in  these  specimens  there 
are  only  certain  planes  in  the  given  direction  along  which  the 
mineral  will  break.  In  the  case  of  cleavage,  every  specimen  of  the 
mineral  will  in  general  show  it,  and  it  can  be  produced  in  a  given 
direction  in  all  parts  of  a  crystal.  Familiar  examples  of  part- 
ing are  the  cases  of  the  octahedral  parting  of  magnetite,  the  basal 
parting  of  pyroxene  and  the  rhombohedral  parting  of  corundum. 
3.  Fracture.  By  the  fracture  of  a  mineral  is  meant  the  way 
in  which  it  breaks  when  it  does  not  show  plane  surfaces  as  in 

cleavage  or  parting.  The  fol- 
lowing terms  are  commonly 
used  to  designate  different  sorts 
of  fracture : 

a.  Conchoidal.  When  the 
fracture  has  smooth,  curved 
surfaces  like  the  interior  surface 
of  a  shell  it  is  said  to  be  con- 
choidal  (see  Fig.  190).  This 
pis  most  commonly  observed 

Fig.  190.    Conchoidal    Fracture  —  Vol-    in    Such     Substances     as    glaSS, 
canic  Glass.  quartz,  etc. 

b.  Fibrous  or  Splintery.    When  the  mineral  breaks  showing 
splinters  or  fibers. 

c.  Hackly.    When  the  mineral  breaks  with  a  jagged,  irregular 
surface  with  sharp  edges. 

d.  Uneven  or  Irregular.    When  the  mineral  breaks  into  rough 
and  irregular  surfaces. 

in.   HARDNESS   OF   MINERALS. 

Minerals  vary  quite  widely  in  their  hardness,  and  a  determi- 
nation of  their  degree  of  hardness  is  often  an  important  aid  to 
their  identification.  A  series  of  minerals  has  been  chosen  as  a 


HARDNESS  OF  MINERALS  61 

scale  by  comparison  with  which  the  relative  hardness  of  any 
mineral  may  be  told.  The  scale  consists  of  crystallized  varieties 
of  the  following  minerals,  each  species  being  harder  than  those 
preceding  it  in  the  scale. 

Scale  of  Hardjiess. 

1.  Talc.                     4.   Fluorite.  8.  Topaz. 

2.  Gypsum.               5.  Apatite.  9.  Corundum. 

3.  Calcite.                 6.   Orthoclase.  10.  Diamond. 

7.   Quartz. 

In  order  to  determine  the  relative  hardness  of  any  mineral  in 
terms  of  this  scale,  it  is  necessary  to  find  which  ones  of  these 
minerals  it  can  and  which  it  cannot  scratch.  In  making  the 
determination  the  following  precautions  should  be  observed: 
Sometimes  when  a  mineral  is  softer  than  another,  portions  of 
the  first  will  leave  a  mark  on  the  second  which  may  be  mis- 
taken for  a  scratch.  It  can  be  rubbed  off,  however,  while  a 
true  scratch  will  be  permanent.  Some  minerals  are  frequently 
altered  on  the  surface  to  material  which  is  much  softer  than  the 
original  mineral.  A  fresh  surface  of  the  specimen  to  be  tested 
should  therefore  be  used.  Sometimes  the  physical  structure  of 
a  mineral  may  prevent  a  correct  determination  of  its  hardness. 
For  instance,  if  a  mineral  is  pulverulent,  granular  or  splintery 
in  its  structure,  it  may  be  broken  down  and  apparently  scratched 
by  a  mineral  much  softer  than  itself.  It  is  always  advisable 
when  making  the  hardness  test  to  confirm  it  by  reversing  the 
order  of  procedure. 

The  following  materials  may  serve  in  addition  to  the  above 
scale:  The  finger  nail  is  a  little  over  2  in  hardness,  since  it  can 
scratch  gypsum  and  not  calcite.  A  cent  is  about  3  in  hardness, 
since  it  can  just  scratch  calcite.  The  steel  of  an  ordinary  pocket- 
knife  is  just  over  5,  and  ordinary  window  glass  has  a  hardness  of 
5.5. 

Crystals  frequently  show  different  degrees  of  hardness,  depend- 
ing upon  the  direction  in  which  they  are  scratched.  Ordinarily 
the  difference  is  so  small  that  it  can  be  detected  only  by  the  use 
of  delicate  instruments. 


62  MANUAL  OF  MINERALOGY 


IV.   TENACITY   OF   MINERALS. 

The  following  terms  are  used  to  describe  various  kinds  of 
tenacity  in  minerals : 

1.  Brittle.     When  a  mineral  breaks  or  powders  easily. 

2.  Malleable.     When  a  mineral  can  be  hammered  out  into 
thin  sheets. 

3.  Sectile.     When  a  mineral  can  be  cut  into  thin  shavings 
with  a  knife. 

4.  Flexible.     When  a  mineral  bends  but  does  not  resume  its 
original  shape  when  the  pressure  is  released. 

5.  Elastic.     When,  after  being  bent,  the  mineral  will  resume 
its  original  position  upon  the  release  of  the  pressure. 


V.   SPECIFIC   GRAVITY   OF  MINERALS. 

The  specific  gravity  of  a  mineral  is  a  number  which  expresses 
the  ratio  existing  between  its  weight  and  the  weight  of  an  equiva- 
lent volume  of  water.  If  a  mineral  has  a  specific  gravity  of  2, 
it  means  that  a  given  specimen  of  that  mineral  weighs  twice 
as  much  as  the  same  volume  of  water.  The  specific  gravity  of 
a  mineral  which  does  not  vary  in  its  composition  is  a  constant 
factor,  the  determination  of  which  is  frequently  an  important 
aid  to  its  identification. 

After  a  little  experience  one  can  frequently  judge  quite  accu- 
rately the  specific  gravity  of  a  mineral  by  weighing  it  in  the  hand. 
Minerals  containing  the  heavy  metals  like  lead,  copper,  iron,  etc., 
can  be  at  once  differentiated  from  those  containing  lighter  ele- 
ments by  this  means.  And  by  practice  one  can  become  expert 
enough  to  be  able  to  distinguish  from  each  other  minerals  that 
have  comparatively  small  differences  in  specific  gravity;  for 
instance,  topaz  (sp.  gr.  =  3.52)  from  orthoclase  (sp.  gr.  =  2.57), 
and  fluorite  (sp.  gr.  =  3.18)  from  quartz  (sp.  gr.  =  2.6). 

'In  order  to  accurately  determine  the  specific  gravity  of  a 
mineral,  the  following  conditions  must  be  observed :  The  mineral 
must  be  pure.  It  must  also  be  solid,  with  no  cracks  or  cavities 


SPECIFIC  GRAVITY  OF  MINERALS 


63 


within  which  bubbles  or  films  of  air  could  be  imprisoned.  The 
fragment  used  should  be  reasonably  large,  about  one  cubic  inch 
being  a  convenient  size.  If  these  conditions  cannot  be  met, 
it  is  of  little  use  to  attempt  a  specific  gravity  determination  by 
any  rapid  and  simple  method. 

The  necessary  steps  in  making  an  ordinary  specific  gravity 
determination  are  briefly  as  follows :  The  mineral  is  first  weighed 
in  air.  Let  this  weight  be  represented  by  x.  It  is  then  immersed . 
in  water  and  weighed  again.  Under  these  conditions  it  weighs 
less,  since  any  object  immersed  in  water  is  buoyed  up  by  a  force 
equivalent  to  the  weight  of  the  water  displaced.  Let  the  weight 
in  water  be  represented  by  y.  Then  x  —  y  equals  the  loss  of 
weight  caused  by  immersion  in  water,  or  the  weight  of  an  equal 

volume  of  water.    The  expression  — - —  will  therefore  yield  a 

x-y 

number  which  is  the  specific  gravity  of  the  mineral. 

The  specific  gravity  of  a  mineral  may  be  determined  in  various 
ways,  those  most  commonly  used 
being  described  below. 

1.  By  Means  of  a  Chemical 
Balance.  The  most  accurate 
method  of  determining  the  specific 
gravity  of  a  mineral  is  by  the  use 
of  a  chemical  balance.  To  one 
beam  of  the  balance  is  suspended 
a  wire  basket  which  is  so  arranged 
that  it  can  be  immersed  in  a  beaker 
of  water  (see  Fig.  191).  The  bas- 
ket is  hung  in  the  water  and  then 
counterbalanced  by  weights  on  the 
opposite  pan  of  the  balance.  The 
mineral  specimen  to  be  tested,  hav- 
ing been  first  weighed  on  the  bal- 
ance in  the  ordinary  fashion,  is  now 
placed  in  the  basket  under  the  water  Flg>  191< 

and  weighed  again.  These  two  weights  are  the  necessary  data 
for  calculating  the  specific  gravity  as  explained  above. 


64 


MANUAL  OF  MINERALOGY 


2.  By  Means  of  a  Jolly  Balance.    Fig.  192  represents  the  bal- 
ance of  Jolly,  by  which  the  specific  gravity  is  measured  through 

the  stretching  of  a  spiral  wire  spring.  From 
the  spring  is  suspended  two  small  metal  pans 
(c  and  d),  one  above  the  other.  The  ap- 
paratus is  so  arranged  that  the  lower  pan 
(d)  is  always  immersed  in 'a  beaker  of  water 
which,  resting  upon  the  adjustable  platform 
B,  can  be  placed  at  any  required  height.  On 
the  side  of  the  upright  A,  which  faces  the 
spiral  wire,  there  is  a  mirror  with  a  gradu- 
ated scale  engraved  upon  it.  The  position 
of  the  balance  is  determined  by  means  of  a 
small  bead  (m)  which  is  strung  on  the  wire 
above  the  upper  pan  and  which  serves  as  an 
indicator.  The  eye  is  brought  into  such  a 
position  that  the  bead  exactly  covers  its 
image  in  the  mirror,  and  its  position  is  then 
determined  by  means  of  the  scale. 

Three  readings  must  be  taken :  first,  simply 
the  position  of  the  balance  with  the  lower 
Fig.  192.  pan  in  the  water,  x\   second,  its  position 

when  the  mineral  is  placed  in  the  upper  pan,  y;  and  third,  its 
position  when  the  mineral  is  in  the  lower  pan  and  covered  with 
water,  z.  The  platform  B  with  the  beaker  of  water  must  be 
properly  adjusted  for  each  of  these  readings  so  as  to  always  have 
the  lower  pan  immersed  in  the  water.  The  expression  x  —  y 
will  give  a  number  representing  the  weight  of  the  mineral  in  air, 
while  x  —  z  will  yield  a  number  corresponding  to  its  weight  in 
water.  From  these  values  the  specific  gravity  of  the  mineral 
can  be  calculated  as  described  above. 

3.  By  Means  of  a  Beam  Balance.     This  is  a  very  convenient 
and  quite  accurate  method  of  determining  specific  gravity.    The 
balance  illustrated  in  Fig.  193  was  devised  by  S.  L.  Penfield, 
who  describes  its  operation  as  follows: 

"The  beam  of  wood  is  supported  on  a  fine  wire,  or  needle,  at 
6  and  must  swing  freely.     The  long  arm  be  is  divided  into  a 


PROPERTIES  DEPENDING  UPON  LIGHT          65 

decimal  scale,  commencing  at  the  fulcrum  6;  the  short  arm  car- 
ries a  double  arrangement  of  pans  so  suspended  that  one  of  them 
is  in  the  air  and  the  other  in  water.  A  piece  of  lead  on  the  short 
arm  serves  to  almost  balance  the  long  arm,  and,  the  pans  being 
empty,  the  beam  is  brought  to  a  horizontal  position,  marked 
upon  the  upright,  near  c,  by  means  of  a  rider  d.  A  number  of 
counterpoises  are  needed,  which  do  not  have  to  be  of  any  specific 


Fig.  193. 

denomination,  as  it  is  their  position  on  the  beam  and  not  their 
actual  weight  which  is  recorded.  The  beam  being  adjusted  by 
means  of  the  rider  d,  a  fragment  of  the  mineral  is  placed  in  the 
upper  pan  and  a  counterpoise  is  chosen,  which,  when  placed 
near  the  end  of  the  long  arm,  will  bring  it  into  a  horizontal 
position.  The  weight  of  the  mineral  in  air  is  given  by  the  posi- 
tion of  the  counterpoise  on  the  scale.  The  mineral  is  next 
transferred  to  the  lower  pan,  and  the  same  counterpoise  is 
brought  nearer  the  fulcrum  b  until  the  beam  becomes  again 
horizontal,  when  its  position  gives  the  weight  of  the  mineral  in 
water."  From  these  two  values  the  specific  gravity  of  the  min- 
eral can  be  calculated. 

VI.   PROPERTIES  DEPENDING  UPON  LIGHT. 
A.   Luster. 

The  luster  of  a  mineral  is  its  appearance  due  to  the  effect  of 
light  upon  it.  In  general  we  divide  minerals  into  three  classes 
depending  upon  their  luster,  namely,  metallic  luster,  submetallic 


66  MANUAL  OF  MINERALOGY 

luster  and  nonmetallic  luster.  A  mineral  having  the  appearance 
of  a  metal  like  lead  or  copper  is  said  to  have  a  metallic  luster. 
The  term  is  further  defined  by  saying  that  a  mineral  with  a 
metallic  luster  is  strictly  opaque  to  light  when  examined  on  its 
thinnest  edges.  The  metallic  luster  of  a  mineral  can  be  proved 
by  observing  the  color  of  its  powder.  If  the  powder  is  black 
or  very  dark  in  color,  it  means  that  each  little  particle  of  the 
mineral  is  still  opaque  to  light,  and  therefore  the  mineral  has  a 
metallic  luster.  This  test  is  made  usually  by  the  aid  of  what 
is  called  a  streak  plate.  This  consists  of  a  piece  of  unglazed 
white  porcelain  upon  which  the  mineral  is  rubbed  so  that  a 
streak  of  its  powder  is  formed  upon  the  plate.  The  color  of  this 
" streak"  of  the  mineral,  as  it  is  called,  will  determine  its  luster 
and  also  frequently  will  materially  help  in  its  identification. 
Examples  of  minerals  with  metallic  luster  would  be,  galena, 
PbS,  with  a  bluish  gray  streak;  pyrite,  FeS2,  with  a  black  streak; 
chalcopyrite,  CuFeS2,  with  a  greenish  black  streak;  and  hema- 
tite, Fe203,  with  a  dark  reddish  brown  streak. 

Nonmetallic  Luster.  Minerals  with  a  nonmetallic  luster  are 
transparent  to  light  on  their  thin  edges.  In  general  they  are 
light  colored,  but  not  necessarily  so.  When  a  streak  is  obtained 
from  a  nonmetallic  mineral,  it  is  either  colorless  or  very  light,  in 
color.  Various  descriptive  terms  are  used  to  further  describe 
the  appearance  of  nonmetallic  minerals,  the  more  common  being 
as  follows: 

Vitreous.     Having  the  luster  of  glass.     Example,  quartz. 

Resinous.  Having  the  appearance  of  resin.  Example,  sphal- 
erite. 

Pearly.  Having  the  appearance  of  pearl.  This  is  usually 
observed  in  minerals  on  surfaces  that  are  parallel  to  cleavage 
planes.  Example,  basal  plane  on  apophyllite. 

Greasy.  Looking  as  if  covered  with  a  thin  layer  of  oil.  Ex- 
amples, some  specimens  of  sphalerite  and  massive  quartz. 

Silky.  Like  silk.  It  is. the  result  of  a  fine  fibrous  structure. 
Examples,  fibrous  malachite,  serpentine,  etc. 

Adamantine.  Having  a  hard,  brilliant  luster  like  that  of  a 
diamond.  It  is  due  to  the  mineral's  high  index  of  refraction 


PROPERTIES  DEPENDING   UPON  LIGHT  67 

(see  p.  71).    The  transparent  lead  minerals,  like  cerussite  and 
anglesite,  show  it. 

Submetallic  Luster.  There  is  no  sharp  divisional  line  between 
minerals  with  metallic  and  those  with  nonmetallic  luster,  and  the 
group  of  minerals  lying  between  is  said  to  have  a  submetallic 
luster.  They  show  a  colored  streak,  but  one  which  is  not  black 
or  very  dark  in  color.  Examples  of  minerals  with  submetallic 
luster  are  limonite  and  some  of  the  darker  varieties  of  sphalerite. 

B.  Color  of  Minerals. 

The  color  of  minerals  is  one  of  their  most  important  physical 
properties.  In  the  case  of  many  minerals,  especially  those 
showing  a  metallic  luster,  color  is  a  definite  and  constant  prop- 
erty and  will  serve  as  an  important  means  of  identification. 
For  example,  the  brass-yellow  col6r  of  chalcopyrite,  the  blue- 
gray  of  galena,  the  black  of  magnetite,  the  green  of  malachite, 
etc.,  is  in  each  case  a  striking  property  of  the  mineral.  It  is  to 
be  noted,  however,  that  surface  alterations  may  change  the  color 
even  in  minerals  whose  color  is  otherwise  constant.  This  is 
shown  in  the  yellow  tarnish  frequently  observed  on  pyrite  and 
marcasite,  the  purple  tarnish  on  bornite,  etc.  In  noting  the 
color  of  a  mineral,  therefore,  a  fresh  surface  should  be  examined. 
Many  minerals,  however,  do  not  show  a  constant  color  in  their 
different  specimens.  This  variation  in  color  in  the  same  species 
may  be  due  to  different  causes.  A  change  in  color  is  often  pro- 
duced by  a  change  in  composition.  The  progressive  isomor- 
phous  replacement  of  zinc  by  iron  in  sphalerite  (see  page  77) 
will  change  its  color  from  white  through  yellow  and  brown  to 
black.  The  minerals  of  the  Amphibole  Group  show  a  similar 
variation  in  color.  The  amphibole  tremolite,  which  is  a  silicate 
with  only  calcium  and  magnesium  as  bases,  is  very  light  in  color, 
at  times  almost  white;  while  actinolite  and  hornblende,  which 
are  amphiboles  that  contain  increasing  amounts  of  iron,  range  in 
color  from  green  to  black.  Again,  a  mineral  may  show  a  wide 
range  of  color  without  any  apparent  change  in  composition. 
Fluorite  is  a  striking  example  of  this,  since  it  is  found  in  crystals 
that  are  colorless,  white,  pink,  yellow,  blue,  green,  etc.  Such 


68  MANUAL  OF  MINERALOGY 

extreme  cases  are,  however,  rare.  Minerals  are  also  frequently 
colored  by  various  impurities.  The  red  variety  of  quartz,  known 
as  jasper,  is  colored  by  small  amounts  of  hematite.  From  the 
above  it  is  seen  that,  while  the  color  of  a  mineral  is  one  of  its  im- 
portant physical  properties,  it  is  not  always  constant,  and  must 
therefore  often  be  used  with  some  caution  in  the  identification 
of  a  species. 

Play  of  Colors.  Iridescence,  Opalescence,  etc.  A  mineral  is 
said  to  show  a  play  of  colors  when  on  turning  it  several  prismatic 
colors  are  seen  in  rapid  succession.  This  is  to  be  seen  especially 
in  the  diamond  and  precious  opal.  A  mineral  is  said  to  show 
a  change  of  color  when  on  turning  it  the  colors  change  slowly, 
being  different  for  varying  positions.  This  is  observed  in  labra- 
dorite.  A  mineral  is  iridescent  when  it  shows  a  series  of  pris- 
matic colors  in  the  interior  of  the  crystal  or  on  the  surface.  It 
is  usually  caused  by  the  presence  of  small  fractures  or  cleavage 
planes  which  serve  to  break  up  the  light  into  the  prismatic  colors. 
Opalescence  is  a  milky  or  pearly  reflection  from  the  interior  of 
a  specimen.  It  is  observed  at  times  in  opal  and  cat's-eye.  A 
mineral  is  said  to  show  a  tarnish  when  the  color  of  the  surface 
differs  from  that  of  the  interior. 

Asterism.  Some  crystals,  especially  those  of  the  Hexagonal 
System,  when  viewed  in  the  direction  of  the  vertical  axis,  present 
starlike  rays  of  light.  This  arises  from  peculiarities  of  texture 
along  the  axial  directions,  or  from  some  inclusions.  A  remark- 
able example  is  the  star  sapphire. 

Phosphorescence.  Several  minerals  when  rubbed  or  heated 
give  out  light.  This  property  is  known  as  phosphorescence. 
Fluorite  often  shows  phosphorescence  when  fragments  are  gently 
heated.  The  color  of  the  emitted  light  may  be  green,  purple, 
rose,  yellow,  etc. 

C.  Refraction  of  Light  in  Minerals. 

When  light  comes  into  contact  with  a  transparent  mineral, 
part  of  it  is  reflected  from  the  surface  of  the  mineral  and  part 
enters  the  mineral.  The  light  which  enters  the  mineral  is  in 
general  refracted.  When  light  passes  from  a  rarer  into  a  denser 


PROPERTIES  DEPENDING  UPON  LIGHT 


69 


medium,  as  in  the  case  of  passing  from  air  into  a  mineral,  its 
velocity  is  retarded.  This  change  in  velocity  is  accompanied 
by  a  corresponding  change  in  the  direction  in  which  the  light 
travels,  and  it  is  this  change  in  direction  of  propagation  that  is 
known  as  refraction  of  light.  The  amount  of  refraction  of  a 
given  light  ray  is  directly  proportional  to  the  ratio  existing  be- 
tween the  velocity  of  light  in  air  and  in  the  mineral.  The  ratio 
between  these  two  velocities  is  known  as  the  index  of  refraction 
of  the  mineral  and  is  designated  by  n.  That  is,  if  the  index  of 
refraction,  or  n,  of  a  mineral  is  2,  light  will  travel  in  it  with  one- 
half  the  velocity  it  has  in  air. 

In  Fig.  194  let  M-M  represent  the  surface  of  a  crystal  of  flu- 
orite.  Let  N-0  be  normal  to  that  surface.  Let  A-0  be  one  of 
a  number  of  parallel  light  rays  striking  the  surface  M-M  in  such 
a  way  as  to  make  the  angle  i  (angle  of  incidence)  with  the  normal 


Fig.  194. 


Refraction  of  Light. 


Fig.  195. 


N-0.  Let  0-P  be  at  right  angles  to  the  rays  and  representing  the 
wave  front  of  the  light  in  air.  As  the  crystal  is  the  denser  me- 
dium the  light  will  travel  in  it  more  slowly.  Therefore,  as  each 
ray  in  turn  strikes  the  surface  M-M,  it  will  be  retarded  and  the 
direction  of  its  path  be  changed  proportionately.  In  going  from 
a  rarer  into  a  denser  medium,  the  direction  of  the  ray  will  be  bent 
toward  the  normal  N-O.  To  find  the  direction  of  the  rays  and 
line  of  wave  front  in  the  crystal,  proceed  as  follows:  Since  the 


70  MANUAL  OF  MINERALOGY 

index  of  refraction  of  fluorite  is  1.43,  ray  A  will  travel  in  the 

crystal,  in  the  time  it  takes  ray  C  to  travel  from  P  to  R,  •——-  of 

1.43 

that  distance,  or  to  some  point  on  the  circular  arc  the  length  of 

whose  radius  OA'  is  — —  the  distance  P-R.     Similarly,  ray  B 
I  A3 

will  travel  in  the  mineral  during  the  period  of  time  in  which 

ray  C  travels  from  S  to  R  a  distance  equal  to  -— -  of  the  distance 

1.43 

S-R,  or  the  radius  TBf.  The  same  reasoning  will  hold  true  for 
all  other  rays.  The  wave  front  in  the  crystal  can  then  be  de- 
termined by  drawing  a  tangent  —  the  line  A'B'R  —  to  these 
various  circular  arcs;  and  lines  perpendicular  to  this  wave  front 
will  represent  the  direction  in  which  the  light  travels  in  the  min- 
eral, and  the  angle  NO  A'  or  r  will  be  the  angle  of  refraction. 
Fig.  195  shows  the  same  construction  as  that  of  Fig.  194,  only 
in  this  case  the  mineral  in  question  is  assumed  to  be  diamond. 
Since  the  index  of  refraction  of  diamond  (n  =  2.42)  is  much 
greater  than  that  of  fluorite,  light  will  travel  in  it  with  a  still 
slower  velocity.  Consequently  in  diamond  the  amount  of  re- 
fraction will  be  greater.  This  is  shown  in  the  two  figures,  in 
both  of  which  the  angle  of  incidence  is  the  same. 

The  refractive  power  toward  light  which  a  mineral  possesses 
has  often  a  distinct  effect  upon  the  appearance  of  the  mineral. 
For  example,  a  mass  of  cryolite  may  almost  always  be  told  at 
sight,  though,  as  is  generally  the  case,  there  is  no  crystal  shape 
to  aid  in  the  identification.  The  mass  has  a  peculiar  appearance, 
something  like  that  of  wet  snow,  and  quite  different  from  that 
of  ordinary  white  substances ;  and  this  is  due  to  the  fact  that  the 
index  of  refraction  of  cryolite  is  unusually  low  for  a  mineral. 
An  instructive  experiment  may  be  tried  by  finely  pulverizing 
some  pure  white  cryolite  and  throwing  the  powder  into  water, 
when  it  will  apparently  disappear,  as  if  it  had  instantly  gone  into 
solution.  The  powder,  however,  is  insoluble,  and  may  be  seen 
indistinctly  as  it  settles  to  the  bottom  of  the  vessel.  The  reason 
for  this  disappearance  of  the  cryolite  is  that  its  index  of  refraction 
(about  1.34)  is  near  that  of  water  (1.335),  hence  the  light  travels 
almost  as  readily  through  the  mineral  as  through  water,  and 
consequently  it  undergoes  little  reflection  or  refraction. 


PROPERTIES  DEPENDING  UPON  LIGHT 


71 


Substances  having  an  unusually  high  index  of  refraction  have 
an  appearance  which  it  is  hard  to  define,  and  which  is  generally 
spoken  of  as  adamantine  luster.  This  kind  of  luster  may  be  com- 
prehended best  by  examining  specimens  of  diamond  (n  —  2.419) 
or  of  cerussite  (n  =  about  3.2).  They  have  a  flash  and  quality, 
some  diamonds  almost  a  steel-like  appearance,  which  is  not 
possessed  by  minerals  of  low  index  of  refraction;  compare,  for 
example,  cerussite  and  fluorite  (n  —  1.434).  It  is  their  high 
index  of  refraction  that  gives  to  many  gem  minerals  their  great 
brilliancy  and  charm. 

In  the  majority  of  cases  the  index  of  refraction  of  a  mineral 
is  not  far  from  1.5,  and  gives  to  minerals  a  luster  which  is  desig- 
nated as  vitreous.  Quartz  (n  =  1.55),  feldspar  (n  =  1.52)  and 
calcite  (n  =  1.57)  are  good  examples. 

D.  Double  Refraction  in  Minerals. 

All  minerals  except  those  belonging  to  the  Isometric  System 
show  in  general  a  double  refraction  of  light.  That  is,  when  a 
ray  of  light  enters  such 
a  mineral  it  is  broken  up 
into  two  rays,  each  of 
which  travels  with  a  dif- 
ferent velocity  through 
the  mineral.  Since  each 
ray  has  its  own  charac- 
teristic velocity,  it  fol- 
lows that  the  angle  of  re- 
fraction will  be  different 
in  each  case  and  the 
paths  of  the  two  rays  will  ^••^^••^^^^^^^^^^^^^^ 

be   divergent.       In  Other  p^.  196.    Double  Refraction  in  Calcite. 

words,  the  light  has  un- 
dergone double  refraction.  In  the  majority  of  cases  the  amount 
of  this  double  refraction  is  small,  and  the  fact  that  it  exists 
can  only  be  demonstrated  by  special  and  delicate  instruments. 
Calcite,  however,  shows  such  a  strong  double  refraction  that 
it  can  be  easily  observed.  Take  a  cleavage  block  of  clear 
calcite  (Iceland  spar),  for  instance,  and  place  it  over  an 


72  MANUAL  OF  MINERALOGY 

image  marked  on  paper.  The  image  will  appear  double  (see 
Fig.  196). 

The  amount  of  double  refraction,  or  in  other  words  the  amount 
of  divergence  of  the  two  rays,  shown  by  any  mineral  depends, 
first,  upon  the  refracting  power  of  the  mineral,  or  its  strength  of 
birefringence,  as  it  is  called;  second,  upon  the  thickness  of  the 
block  of  the  mineral ;  and  lastly,  upon  the  crystallographic  direc- 
tion in  which  the  light  is  traveling  in  the  mineral.  In  the  case 
of  tetragonal  and  hexagonal  minerals,  there  is  one  direction  (that 
of  the  vertical  crystallographic  axis)  in  which  no  double  refrac- 
tion takes  place.  As  soon  as  a  ray  of  light  in  the  mineral  diverges 
from  this  direction  it  is  doubly  refracted,  and  the  amount  of 
double  refraction  increases  as  the  path  of  the  light  becomes  more 
oblique,  and  attains  its  maximum  when  it  is  at  right  angles  to 
the  vertical  axis.  Such  minerals  belong  to  the  optical  class  known 
as  uniaxial.  In  the  case  of  orthorhombic,  monoclinic  and  triclinic 
minerals,  there  are  two  directions  similar  to  the  one  described 
above,  in  which  no  double  refraction  takes  place,  and  the  minerals 
of  these  systems  are  therefore  spoken  of  as  optically  biaxial. 

In  addition  to  doubly  refracting  light,  all  minerals  except  those 
of  the  Isometric  System  polarize  it  as  well.  Ordinary  light  is 
conceived  as  made  up  of  vibrations  taking  place  in  all  planes. 
Light  is  polarized  when  it  vibrates  in  a  single  plane.  In  the  case 
of  both  uniaxial  and  biaxial  crystals,  each  of  the  two  rays  into 
which  a  beam  of  light  is  refracted  is  polarized  and  in  planes 
which  are  perpendicular  to  each  other.  For  a  fuller  considera- 
tion of  the  optical  properties  of  minerals,  the  reader  must  be 
referred  to  books  of  a  more  detailed  character. 

VII.   PYROELECTRICITY. 

Crystals  of  certain  minerals,  on  cooling  after  being  heated  to 
about  100°  C.,  will  develop  upon  different  portions  a  positive 
and  a  negative  electric  charge.  This  can  be  proved  by  the  power 
that  such  minerals  show  under  these  conditions  to  attract  and 
hold  to  themselves  small  pieces  of  paper,  etc.  Minerals  which 
are  hemimorphic  in  their  crystallographic  character,  like  cala- 
mine,  tourmaline,  etc.,  exhibit  this  property. 


III.   CHEMICAL  MINERALOGY. 

A  MINERAL  may  be  defined  as  a  naturally  occurring  substance 
having  a  definite  chemical  composition.  The  chemical  compo- 
sition of  a  mineral  is  the  most  fundamentally  important  fact 
about  it,  for  upon  this  all  its  other  properties  must  in  great 
measure  be  dependent.  The  physical  characteristics  of  a  mineral 
may  sometimes  serve  as  means  of  its  positive  identification,  and 
in  the  great  majority  of  cases  they  will  be  of  material  assistance; 
but  the  final  proof  of  its  identity  will  more  often  lie  in  the  deter- 
mination of  its  chemical  character  by  means  of  chemical  tests. 
Consequently  the  study  of  the  chemistry  of  minerals  is  the  most 
important  single  division  of  the  subject.  This  section  will, 
therefore,  be  devoted  to  a  brief  and  elementary  discussion  of 
chemical  mineralogy.  First  some  general  aspects  of  the  subject 
will  be  presented,  followed  by  a  short  description  of  the  methods 
of  testing  for  the  different  elements  most  commonly  observed. 
The  scope  and  size  of  this  book  necessitate  the  assumption  that 
the  reader  is  familiar  with  at  least  the  essentials  of  chemical  fact 
and  nomenclature. 

Scientists  up  to  the  present  time  have  established  the  occur- 
rence of  more  than  eighty  different  elements.  The  greater  part 
of  these,  however,  are  extremely  rare  and  are  only  of  scientific 
interest.  Some  forty-four  elements  are  found  in  sufficient 
amount,  or  because  of  their  properties  are  of  sufficient  impor- 
tance, to  warrant  a  discussion  of  them  here.  A  considerable 
proportion  of  this  list  also  must  "be  considered  as  rare  in  occur- 
rence. The  following  table  gives  the  names  and  symbols  of  the 
eighteen  most  common  elements  arranged  in  the  approximate 
order  of  their  importance  as  constituents  of  the  earth's  crust: 

73 


T4  MANUAL  OF  MINERALOGY 

Oxygen          0.  Sodium         Na.        Phosphorus    P. 


Silicon            Si. 
Aluminium    Al. 
Iron               Fe. 
Calcium         Ca. 
Magnesium    Mg. 

Potassium    K. 
Hydrogen     H. 
Titanium      Ti. 
Carbon         C. 
Chlorine        Cl. 

Sulphur           S. 
Barium           Ba. 
Manganese     Mn. 
Strontium       Sr. 
Fluorine         F. 

It  is  to  be  noted  that  the  above  list  fails  to  include  such  im- 
portant elements  as  copper,  lead,  zinc,  silver,  gold,  tin,  mercury, 
nickel,  antimony,  arsenic,  etc.,  all  of  which  form  much  less  than 
one-hundredth  of  one  per  cent  of  the  rocks  of  the  earth's  crust. 

These  elements  occur  alone  or  in  various  chemical  combina- 
tions in  the  form  of  minerals.  Below  is  given  a  brief  discussion 
of  the  various  classes  of  chemical  compounds  in  which  the  ma- 
jority of  minerals  occur. 

Chemical  Groups. 

Elements.  There  are  a  few  minerals  that  consist  of  single 
elements  alone.  For  example,  gold,  Au. 

Sulphides.  A  very  important  group  of  minerals,  consisting 
of  combinations  of  the  various  metals  with  the  element  sulphur, 
are  known  as  sulphides.  They  include  the  majority  of  the 
metallic  ore  minerals.  For  example,  pyrite,  FeS2. 

Sulpho-salts.  This  group  of  minerals  includes  a  series  which 
mostly  contain  lead,  copper  or  silver  in  combination  with  sulphur 
and  either  antimony  or  arsenic.  For  example,  tetrahedrite, 
Cu8Sb2S7. 

Haloids.  This  group  includes  minerals  that  are  salts  of  the 
halogen  acids,  chiefly  hydrochloric  or  hydrofluoric  acids.  Ex- 
amples are  halite,  NaCl,  and  fluorite,  CaF2. 

Oxides.  The  minerals  of  this  group  contain  a  metal  in  com- 
bination with  oxygen.  For  example,  hematite,  Fe203. 

Hydroxides.  An  hydroxide  is  a  mineral  that  contains  the 
hydroxyl  group,  OH,  as  an  important  radical.  For  example, 
limonite,  Fe403(OH)6. 

Carbonates.  The  carbonates  are  salts  of  carbonic  acid, 
H2C03.  For  example,  calcite,  CaC03. 


DERIVATION  OF  A   CHEMICAL  FORMULA         75 

Silicates.  The  silicates  form  the  largest  chemical  group  among 
minerals.  They  contain  various  elements  as  bases,  the  most 
common  of  which  are  sodium,  potassium,  calcium,  magnesium, 
aluminium  and  ferrous  and  ferric  iron.  They  are  frequently 
very  complex  in  their  chemical  structure.  They  are  salts  of  a 
number  of  different  silicic  acids,  the  most  important  of  which 
are  as  follows: 

Orthosilicate  acid  =  H4Si04,  which  is  represented  by  alman- 
dite,  Fe3Al2(Si04)3. 

Metasilicic  acid  =  H4Si206  or  H2Si03,  represented  by  leucite, 
KAl(Si03)2. 

Polysilicic  acid  =  H4Si308,  represented  by  orthoclase,  KAlSi308. 

Niobates  and  Tantalates.  These  are  combinations  of  vari- 
ous metals  with  the  rare  niobic'and  tantalic  acids.  For  example, 
columbite,  FeNb206,  and  tantalite,  FeTa206. 

Phosphates.  The  phosphates  are  salts  of  some  phosphoric 
acid.  The  most  common  member  of  the  group  is  the  mineral 
apatite,  Ca4(CaF)  (P04)3. 

Sulphates.  The  sulphates  are  salts  of  sulphuric  acid,  H2S04. 
For  example,  gypsum,  CaS04.2H20. 

Tungstates.  These  are  salts  of  the  rare  tungstic  acid  H2W04. 
For  example,  scheelite,  CaW04. 

Derivation  of  a  Chemical  Formula  from  the  Analysis  of 
a  Mineral. 

The  chemical  formulas  which  are  assigned  to  minerals  have  in 
every  case  been  calculated  from  chemical  analyses.  An  analysis 
gives  the  percentage  composition  of  a  mineral,  or,  in  other  words, 
the  parts  by  weight  in  one  hundred  of  the  different  elements  or 
radicals  present.  Consider  the  following  analysis  of  chalcopy- 
rite: 

Percentages.     Atomic  weights.  Ratio. 

S  =  34.82    ^         32.06  =  1.086  =  2.00 

Gu  =  34.30    -r-         63.6  =  0.539  =  0.99  or  1.00 

Fe  =  30.59    -r-         55.9  =  0.547  =  1.00 

99.71 

The  percentage  numbers  given  indicate  the  proportions  by 

weight  of  the  different  elements  in  the  mineral.    But  as  these 


76  MANUAL  OF  MINERALOGY 

elements  have  different  atomic  weights,  the  numbers  do  not 
represent  the  ratio  of  the  different  atoms  to  each  other  in  the 
chemical  molecule.  In  order  to  derive  the  relative  proportions 
of  the  atoms  of  the  different  elements  to  each  other,  the  percent- 
ages as  given  are  divided  in  each  case  by  the  atomic  weight  of 
the  element.  This  gives  a  series  of  numbers  which  does  repre- 
sent the  ratio  of  the  atoms  to  each  other  in  the  molecule.  In  the 
analysis  of  chalcopyrite  this  ratio  becomes  S  :  Cu  :  Fe  =  2  : 1  ;  1. 
Consequently  CuFeS2  will  constitute  the  chemical  formula  for 
the  mineral. 

If  the  mineral  is  an  oxygen  compound  the  results  of  the  analy- 
sis are  given  as  percentages  of  the  oxides  present,  and  by  a  cal- 
culation similar  to  that  outlined  above  the  ratio  of  these  oxide 
radicals  to  each  other  in  the  molecule  is  determined;  the  only 
difference  in  the  process  being  that  in  this  case  the  percentage 
numbers  are  divided  by  the  sum  of  the  atomic  weights  of  the 
elements  present  in  the  different  radicals.  As  an  example  con- 
sider the  following  analysis  of  gypsum: 

Percentages.      Molecular  weights.  Ratio. 

SO3  =  46.61    -r-          83.06  =  0.583  =  1.00 

CaO  =  32.44    +          56.1  =  0.578  =  0.99  or  1.00 

H2O  =  20.74    +          18.0  =  1.152  =  1.98  or  2.00 
99.79 

From  this  it  is  seen  that  the  ratio  of  the  radicals  to  each  other 
in  the  molecule  is  S03  :  CaO  :  H20  =  1  :  1  :  2,  and  consequently 
the  composition  of  gypsum  can  be  represented  by  the  formula 
CaO.S03.2H20  or  CaS04.2H20. 

Calculation  of  the  Percentage  Composition  of  a  Mineral 
from  Its  Chemical  Formula. 

It  frequently  happens  that  it  is  desirable  to  determine  what 
the  theoretical  composition  of  a  mineral  is,  having  given  its 
formula.  The  process  of  calculation  is  the  reverse  of  that 
described  in  the  preceding  division.  Take,  for  example,  the 
mineral  chalcopyrite,  CuFeS2;  what  are  the  proportions  by 
weight  of  the  different  elements  in  one  hundred  parts  of  the 
mineral?  The  process  consists  in  first  adding  up  the  atomic 


ISOMORPHISM 


77 


weights  of  the  different  elements  present  and  so  obtaining  the 
molecular  weight  of  the  compound,  as  follows: 

Atomic  weights. 
Cu  =  63.6 

Fe  =  55.9 

S     =  32.06  X  2  =  64.12 
Molecular  weight  CuFeS2  =  183.62 

It  is  obvious  from  the  above  that  in  183.62  parts  by  weight  of 
chalcopyrite  there  are  63.6  parts  of  copper,  etc.  In  order  to  find 
the  parts  of  copper  in  100  parts  of  the  mineral,  or  in  other  words, 
its  percentage,  the  following  proportion  is  made: 

183.62  :  63.6  =  100  :  x. 

When  this  equation  is  solved,  x  becomes  34.64,  or  the  percent- 
age of  copper  in  chalcopyrite.  The  percentages  of  the  iron  and 
sulphur  are  to  be  obtained  in  a  similar  manner. 

Isomorphism. 

It  is  to  be  noted  frequently  that  the  results  of  a  mineral  analy- 
sis do  not  agree  with  the  theoretical  composition  of  the  mineral 
as  calculated  from  its  formula.  Further,  it  often  happens  that 
the  analyses  of  different  specimens  of  the  same  mineral  will 
show  marked  variations  in  the  proportions  of  the  different  ele- 
ments present.  If  the  material  analyzed  was  pure  and  the  analy- 
sis accurately  made,  these  variations  are  commonly  to  be  ex- 
plained by  the  principle  of  isomorphism.  To  make  clear  what 
is  meant  by  this  term,  it  will  be  best  to  consider  some  illustrative 
examples.  Sphalerite,  for  instance,  is  a  mineral  which  shows  in 
its  different  specimens  a  wide  range  in  color,  from  white  through 


I. 

At.  Ra- 

wt.  tio. 

II. 

At.      Ra- 
wt.      ti9- 

III. 

At.      .Ra- 
wt.       tio. 

S  =32.22 
Zn  =67.46 
Fe=  
Cd  =  .  .  . 

32.06=1.00 
65.4  =1.03 

33.36 
63.36 
3.60 

32.06=1.04     =1.00 
65.4  =0.96)      ,  ft9 
55.9  =0.06)      L-v 

33.25 
50.02 
15.44 
0.30 

32.06=1.037     =1.0 
65.4  =0.764] 
55.9  =0.2761      .  mft 
112.4  =0.0021  -1-018 

Pb=  . 

1.01 

206.9  =0  004J 

Total....  99.  68 

100  32 

100.02 

78  MANUAL  OF  MINERALOGY 

brown  to  black,  with  a  corresponding  variation  in  composition. 
In  column  I  is  given  an  analysis  of  white  sphalerite  from  Frank- 
lin Furnace,  N.  J.,  in  column  II  is  given  an  analysis  of  a  brown 
sphalerite  from  Roxbury,  Conn.,  and  in  column  III  that  of  a 
black  sphalerite  from  Felsobanya. 

It  will  be  noted  that  in  the  three  analyses  there  is  a  progressive 
increase  in  the  percentages  of  iron  present  and  a  corresponding 
decrease  in  the  amount  of  zinc.  It  would  appear  as  if  the  iron 
had  replaced  a  portion  of  the  zinc  in  the  mineral  and  was  play- 
ing the  same  part  as  the  zinc  in  the  molecule.  Further,  if  the 
atomic  ratios  are  derived  from  each  analysis  by  the  method  de- 
scribed in  the  preceding  division,  it  will  be  found  that  in  analy- 
ses II  and  III  the  series  of  numbers  do  not  show  any  rational 
relations  to  each  other.  But,  if  the  numbers  derived  in  each 
case  from  the  percentages  of  the  different  metals  present  are 
combined,  their  sum  will  equal  the  number  derived  from  the  per- 
centage of  the  sulphur.  In  other  words,  the  number  of  atoms  of 
zinc  plus  those  of  iron,  lead  and  cadmium  equals  the  number  of 
atoms  of  sulphur.  The  formula  of  sphalerite  could  therefore  be 
written  R"S,  where  R"  equals  chiefly  zinc,  with  smaller  amounts 
of  iron  and  other  metals.  Another  way  of  expressing  the  same 
thing  would  be  (Zn,Fe)S.  In  this  case  the  iron  is  said  to  be 
isomorphous  with  the  zinc,  since  it  has  the  power  to  replace  the 
zinc  in  the  mineral  in  varying  proportions  without  changing  its 
molecular  structure  or  crystal  form. 

The  garnets  form  a  series  of  minerals  with  the  same  crystal- 
lization and  general  physical  properties,  but  show  quite  a  wide 
variation  in  chemical  composition.  Consider  the  following  analy- 
sis of  an  almandine  garnet : 

Percentages.       Molecular  weights.         Ratio. 

SiO2   =  35.92  4-    60.4  =0.594  =3.00 

A12O3  =  19.18  4-  102.2  =  0.187  I  n  917  -  1  no 

Fe203=     4.92  -M59.8  =  0.030     U' 

•FeO   =   29.47  -f-    71.9  =0.409 

MnO=     4.80;  ^    71.0  =0.067 

MgO  =     3.70  +    40.36  =  0.091 

CaO  =     2.38  ^   56.1  =  0.042 
100.37 


0.609  =  3.02 


ISOMORPHISM  79 

It  is  a  silicate  containing  chiefly  ferrous  and  aluminium  oxides 
but  with  smaller  amounts  of  manganese,  magnesium,  calcium  and 
ferric  oxides.  If  the  ratio  of  the  series  of  oxides  to  each  other 
in  the  molecule  is  obtained,  it  is  seen  that  it  is  not  a  rational  one. 
But  if  the  ratio  numbers  of  the  similar  oxides  are  combined,  — 
that  is,  the  number  from  the  A1203  with  that  from  the  Fe203,  and 
that  from  the  FeO  with  those  from  the  MnO,  MgO  and  CaO,— 
it  will  be  found  that  the  relationship  of  the  different  groups  of 
radicals  can  be  expressed  as  Si02  :  A1203  -j-  Fe203  :  FeO  +  MnO 
+  MgO  -f  CaO  =  3:1:3.  From  this  it  is  seen  that  some  of 
the  possible  A1203  has  been  replaced  by  isomorphous  Fe203, 
and  that  a  part  of  the  FeO  has  been  replaced  by  the  isomor- 
phous oxides  of  MnO,  MgO  and  CaO.  The  formula  for  this 
garnet  might  be  written,  therefore,  as  3R//0.1R2///03.3Si02  or 
R3//R2///(Si04)3,  in  which  R"  =  Fe,  Mn,  Mg  and  Ca,  and  R'"  =  A1 
and  Fe. 

Isomorphous  Groups.  A  series  of  compounds  which  have 
analogous  chemical  compositions  and  closely  similar  crystal 
forms  are  said  to  make  an  isomorphous  group.  The  artificial 
compounds  known  as  the  alums  form  a  striking  example.  They 
are  double  salts  of  sulphuric  acid,  similar  to  the  following, 
KA1(S04)2.12H20,  which  is  known  as  potash  alum.  They  may 
vary, in  their  composition  by  the  substitution  of  Na,  Li,  NH4, 
etc.,  for  the  potassium  and  of  Fe"'  and  Cr  for  the  aluminium. 
All  these  compounds  have,  therefore,  different  but  analogous 
compositions,  and  it  is  found  also  that  they  all  crystallize  in  the 
Isometric  System  with  an  octahedral  habit.  Further,  if  a  crys- 
tal of  one  alum  is  suspended  in  a  saturated  solution  of  another 
member  of  the  series,  the  crystal  will  continue  to  grow.  From 
this  it  is  proved  that  the  molecules  of  the  different  alums  are 
physically  so  closely  alike  that  they  can  be  substituted  for  each 
other  in  any  proportion.  Therefore  this  series  of  compounds  is 
said  to  be  an  Isomorphous  Group. 

Many  such  groups  are  to  be  found  in  minerals,  and  attention 
is  called  to  them  in  various  places  in  Section  IV.  Reference 
might  be  made  to  one  of  the  most  prominent  of  these  in  the  case 
of  the  Calcite  Group  (see  page  203).  This  is  a  series  of  minerals 


80  MANUAL  OF  MINERALOGY 

all  of  which  are  carbonates  of  similar  bivalent  metals,  and  there- 
fore they  can  be  said  to  have  analogous  chemical  compositions. 
Further,  they  all  crystallize  in  the  same  crystal  system  and  class, 
and  have  closely  agreeing  angles  between  similar  crystal  faces. 
Consequently  they  conform  to  the  second  requirement  for  an 
Isomorphous  Group,  namely,  that  the  minerals  of  it  should  show 
similar  crystal  forms. 

Dimorphism,  Trimorphism,  Etc. 

A  number  of  cases  are  well  known  among  minerals  in  which 
two  or  three  different  species  have  the  same  chemical  com- 
position but  distinctly  different  physical  properties.  When  one 
compound  appears  in  two  different  forms,  it  is  said  to  be  dimor- 
phous ;  when  in  three  different  forms,  trimorphous.  Carbon  in 
the  forms  of  graphite  and  diamond,  calcium  carbonate  as  calcite 
and  aragonite,  iron  sulphide  as  pyrite  and  marcasite,  are  familiar 
examples  of  dimorphism.  The  two  minerals  in  each  case  differ 
from  each  other  in  such  physical  properties  as  crystallization, 
hardness,  specific  gravity,  color,  reactions  with  acids,  etc.  Ti- 
tanium oxide,  Ti02,  is  trimorphous,  since  it  occurs  in  the  three 
distinct  minerals,  rutile,  octahedrite  and  brookite. 

Instruments,  Reagents  and  Methods  of  Testing. 

The  Blowpipe  and  Its  Use.  Many  of  the  chemical  tests 
made  on  minerals  are  performed  by  aid  of  an  instrument  known 
as  a  blowpipe.  The  blowpipe  consists  essentially  of  a  tapering 
tube  ending  in  a  small  and  symmetrical  opening  through  which 
air  can  be  forced  in  a  thin  stream  at  high  pressure.  This  current 
of  air,  when  directed  into  a  luminous  flame,  converts  it  into  a 
small  and  very  hot  flame,  by  means  of  which  many  important 
tests  can  be  made. 

Fig.  197  represents  a  common  type  of  blowpipe.  The  air  is 
forced  from  the  lungs  into  the  mouthpiece,  c,  which  fits  into  the 
upper  end  of  the  tube  and  issues  from  the  small  opening  at  the 
other  end.  The  tip  of  the  blowpipe,  b,  is  placed  just  within  a 


INSTRUMENTS,  REAGENTS,  ETC. 


81 


flat  flame  which  is  rich  in  carbon,  such  as  is  obtained  from  a 
candle  or  ordinary  illuminating  gas.  A  convenient  method  of 
producing  a  blowpipe  flame  is  to  use  illuminating  gas  in  a  Bunsen 
burner,  in  which  an  inner  tube,  e  (Fig.  198),  has  been  placed  so  as 
to  shut  off  the  supply  of  air  at  the  base  of  the  burner  and  thus 
convert  the  flame  into  a  luminous  one.  The  upper  end  of  this 
tube  is  flattened  and  cut  at  an  angle,  as  is  shown  in  Fig.  198.  The 


Fig.  197. 


Fig.  198. 


gas  flame  is  ordinarily  adjusted  so  that  it  measures  about  1 
inch  in  height  and  \  inch  hi  breadth.  The  blowpipe  is  intro- 
duced into  this  flame  as  shown  in  Fig.  199.  The  resulting  blow- 
pipe flame  should  be  nonluminous,  narrow,  sharp-pointed  and 
clean-cut.  If  illuminating  gas  is  not  available,  a  candle  with  a 
flat  wick  or  even  an  ordinary  candle  can  be  used.  The  latter 
require,  however,  more  skill  in  manipulation. 

The  Art  of  Blowpiping.     It  usually  requires  some  practice 
before  one  can  produce  a  steady  and  continuous  blowpipe  flame. 


82  MANUAL  OF  MINERALOGY 

Many  tests  can  be  made  by  means  of  a  flame  produced  by  ex- 
hausting the  supply  of  air  in  the  lungs  simply  once.  But  fre- 
quently an  operation  takes  a  longer  time  than  this  would, give, 
and  the  interruption  necessary  in  order  to  fill  the  lungs  afresh 
would  materially  interfere  with  the  success  of  the  experiment. 
Consequently  it  often  becomes  important  to  be  able  to  maintain 
a  steady  stream  of  air  from  the  blowpipe  for  a  considerable  time. 
This  is  accomplished  by  distending  the  cheeks  so  as  to  form  a 
reservoir  of  air  in  the  mouth.  When  the  supply  of  air  in  the 
lungs  is  exhausted,  the  passage  from  the  mouth  into  the  throat 


Fig.  199. 

is  closed  by  lifting  the  root  of  the  tongue  and  while  a  new  supply 
is  being  obtained  by  breathing  in  through  the  nose  a  steady 
stream  of  air  is  also  being  forced  out  of  the  reservoir  in  the  mouth. 
In  this  way  a  constant  flame  may  be  obtained.  It  requires, 
however,  considerable  practice  to  do  this  skillfully. 

The  Character  of  the  Blowpipe  Flame.  Fig.  199  represents 
a  typical  blowpipe  flame.  The  inner  cone,  c,  which  is  light  blue 
in  color  and  the  most  distinct  part  of  the  flame,  is  composed  of 
unburned  gas  mixed  with  air  from  the  blowpipe.  There  is  no 
combustion  taking  place  in  this  part  of  the  flame.  Around 
this  cone  is  a  narrow  pale-violet  cone,  b,  which  is  almost 
invisible  and  in  which  the  combustion  does  take  place.  Any 
gas  that  is  used  for  the  production  of  the  flame  will  consist  of 
some  combination  of  carbon  and  hydrogen.  These  elements 
when  the  gas  is  burned  are  converted  into  their  respective  oxides. 
The  hydrogen  burns  directly  to  water  vapor,  H20.  The  carbon 


INSTRUMENTS,  REAGENTS,  ETC.  83 

burns  first  to  its  lower  oxide,  CO,  known  as  carbon  monoxide. 
Later  this  oxide  will  be  changed  by  the  addition  of  another  atom 
of  oxygen  to  the  higher  oxide,  C02,  carbon  dioxide.  The  final 
products  of  the  combustion  will,  therefore,  be  the  gases  H20  and 
C02.  In  cone  b,  where  combustion  is  taking  place,  there  will 
necessarily  be  considerable  amounts  of  the  lower  oxide  of  carbon, 
CO.  Surrounding  cone  b  there  will  be  an  invisible  cone,  a,  con- 
sisting of  the  final  products  of  combustion,  C02  and  H20. 

Fusion  by  Means  of  Blowpipe  Flame.  A  good  blowpipe 
flame  may  reach  a  temperature  as  high  as  2000°  C.  When  skill- 
fully handled  small  pieces  of  fine  platinum  wire  may  be  melted 
in  it.  The  determination  of  the  degree  of  fusibility  of  a  mineral 


Fig.  200. 

is  an  important  aid  to  its  identification.  In  order  to  make  the 
test,  a  small  and  if  possible  a  sharply  pointed  fragment  of  the 
mineral  should  be  inserted  into  the  blowpipe  flame  just  beyond 
the  tip  of  the  inner  cone,  where  the  combustion  is  most  rapid 
and  the  temperature  the  highest.  The  fragment  should  be  held 
as  illustrated  in  Fig.  200,  so  that  it  projects  beyond  the  end  of  the 
forceps  by  which  it  is  held  in  such  a  manner  that  the  entire  heat 
of  the  flame  can  be  concentrated  upon  it.  If  it  melts  and  rounds 
over,  losing  its  sharp  outline,  it  is  said  to  be  fusible  in  the  blow- 
pipe flame.  Minerals  can  therefore  be  divided  into  two  classes, 
as  to  whether  they  are  fusible  or  infusible  in  this  flame.  The 
minerals  which  are  fusible  can  be  further  classified  according  to 


84  MANUAL  OF  MINERALOGY 

the  degree  of  ease  with  which  they  fuse.  To  assist  in  this  classi- 
fication, a  series  of  six  minerals  which  show  different  degrees  of 
fusibility  has  been  chosen  as  a  scale  to  which  all  fusible  minerals 
may  be  approximately  referred.  For  instance,  when  a  mineral 
is  said  to  have  a  fusibility  of  3,  it  means  that  it  will  fuse  with 
the  same  degree  of  ease  as  the  mineral  which  is  listed  as  3  in  the 
scale.  In  making  such  comparative  tests,  it  is  necessary  to  use 
fragments  of  the  same  size  and  to  have  the  conditions  of  the 
experiments  uniform.  The  minerals  of  the  scale  of  fusibility 
are  as  follows :  •  . 

1.  Stibnite.    Very  easily  fusible.    A  small  splinter  will  readily 
melt  in  a  candle  flame. 

2.  Chalcopyrite.    Easily  fusible.    A  small  fragment  will  fuse 
in  the  Bunsen  burner  flame. 

3.  Almandine  Garnet.     Infusible  in  the  Bunsen  burner  flame 
but  fuses  easily  in  the  blowpipe  flame. 

4.  Adinolite.    A  sharp-pointed  splinter  fuses  without  much 
difficulty  in  the  blowpipe  flame. 

5.  Orthoclase.    The  edges  of  a  fragment  are  rounded  at  the 
highest  heat  of  the  blowpipe  flame. 

6.  Enstatite.    Practically  infusible  in  blowpipe  flame,  only 
the  fine  ends  of  sharp-pointed  fragments  being  rounded. 

Reducing  and  Oxidizing  Flames.  Reduction  consists  essen- 
tially in  taking  oxygen  away  from  a  chemical  compound,  and 
oxidation  consists  in  adding  oxygen  to  it.  These  two  opposite 
chemical  reactions  can  be  accomplished  by  means  of  a  blowpipe 
flame.  Cone  6,  Fig.  199,  as  explained  above,  contains  CO,  or  car- 
bon monoxide.  This  is  what  is  known  as  a  reducing  agent,  since, 
because  of  its  strong  tendency  to  take  up  oxygen  in  order  to  be- 
come C02,  or  carbon  dioxide,  it  will,  if  possible,  take  oxygen  away 
from  another  substance  in  contact  with  it.  For  instance,  if  a 
small  fragment  of  the  ferric  oxide  of  iron,  hematite,  Fe203,  is 
held  in  this  part  of  the  blowpipe  flame,  it  will  be  reduced  by  the 
removal  of  one  atom  of  oxygen  to  the  ferrous  oxide,  FeO,  accord- 
ing to  the  following  equation : 

Fe203  -f  CO  =  2FeO  +  C02. 


INSTRUMENTS,  REAGENTS,  ETC.  85 

This  change  can  be  proved  by  noting  that  the  ferric  oxide  is  red 
in  color  and  nonmagnetic,  while  the  ferrous  oxide  is  black  and 
strongly  magnetic.  This  cone  6  is  therefore  known  as  the  re- 
ducing part  of  the  blowpipe  flame,  and  when  it  is  wished  to  per- 
form a  reduction  test  the  mineral  fragment  is  placed  at  r,  as 
shown  in  Fig.  199. 

On  the  other  hand,  if  oxidation  is  to  be  accomplished,  the 
mineral  must  be  placed  entirely  outside  of  the  flame,  where  the 
oxygen  of  the  air  can  have  free  access  to  it,  but  where  it  can  still 
get  in  large  degree  the  heat  of  the  flame.  Under  these  condi- 
tions, if  the  reaction  is  possible,  oxygen  will  be  added  to  the 
mineral  and  the  substance  will  be  oxidized.  The  oxidizing  part  of 
the  blowpipe  flame  is  at  o  (Fig.  199).  Pyrite,  FeS2,  for  instance, 
if  placed  in  the  oxidizing  flame,  would  be  converted  into  ferric 
oxide,  Fe203,  and  sulphur  dioxide,  S02,  according  to  the  following 
equation : 

2FeS2  +  110  =  Fe203  +  4S02. 

The  ferric  oxide  would  form  a  dark-red  residue,  while  the  sulphur 
dioxide  would  come  off  as  a  pungent-smelling  gas. 

Use  of  Charcoal  in  Blowpiping.  Small  charcoal  blocks,  that 
should  best  be  about  4  inches  long,  1  inch  wide  and  |  inch  thick, 


Fig.  201.    An  Oxide  Coating  on  Charcoal. 

are  employed  in  a  number  of  blowpipe  tests.  They  are  used  as 
a  support  upon  which  various  reactions  are  accomplished.  For 
instance,  metals  like  lead,  silver,  copper,  etc.,  may  be  reduced 
from  their  minerals  by  means  of  the  blowpipe  flame,  the  experi- 
ment being  performed  upon  charcoal.  Characteristic  oxide  coat- 
ings also  may  be  obtained  upon  the  surface  of  a  charcoal  block  (see 
Fig.  201).  The  charcoal  should  be  of  a  fine  and  uniform  grain. 
It  should  not  be  so  soft  as  to  readily  soil  the  fingers,  nor  should 
it  be  so  hard  as  not  to  be  easily  cut  and  scraped  by  a  knife. 
The  following  table  gives  a  list  of  the  elements  which  yield 


86 


MANUAL  OF  MINERALOGY 


characteristic  oxide  coatings  when  their  minerals  are  heated  in 
the  oxidizing  flame  on  charcoal: 


Oxide. 

Color  and  character  of 
coating. 

Remarks. 

Arsenious  Oxide. 
Aa203. 

White  and  volatile,  depositing  at 
some  distance  from  the  mineral. 

Usually  accompanied  by 
garlic  odor. 

Antimony  Oxides. 
Sb2O3,  Sb2O4. 

White  and  volatile,  depositing  close 
to  the  mineral. 

Heavier   than  arsenic 
oxide. 

Zinc  Oxide. 
ZnO. 

Yellow  when  hot,  white  when  cold. 
Nonvolatile  in  the  oxidizing  flame. 
Deposits  very  close  to  mineral. 

If  coating  is  moistened 
with  cobalt  nitrate 
and  heated  intensely, 
it  turns  green. 

Tin  Oxide. 
Sn02. 

Faint  yellow  when  hot,  white  when 
cold.  Nonvolatile  in  the  oxidizing 
flame. 

Molybdenum  Oxide. 
Mo03. 

Pale  yellow  when  hot,  white  when 
cold.  Sometimes  crystalline.  Vol- 
atile in  the  oxidizing  flame. 

If  the  coating  is  touched 
for  a  moment  by  a 
reducing  flame,  it  be- 
comes dark  blue. 

Lead  Oxide. 
PbO 

Yellow  near  the  mineral  and  white 
farther  away. 

Coating  at  times  is  com- 
posed of  white  sul- 
phite and  sulphate 
of  lead  in  addition  to 
the  oxide. 

Bismuth  Oxide. 
Bi203. 

Yellow  near  the  mineral  and  white 
farther  away. 

To  be  told  from  the 
lead-oxide  coating  by 
iodine  tests  (see  p.  97). 

Open  Tube  Test.  Glass  tubing  of  hard  glass  is  used  in  mak- 
ing what  are  known  as  open  tube  tests.  The  tubing  should 
be  cut  into  approximately  8-inch  lengths  and  have  an  internal 
diameter  of  |  inch.  An  open  tube  is  used  ordinarily  for  making 
oxidation  tests.  A  small  amount  of  the  mineral  to  be  tested  is 
commonly  powdered  and  placed  in  the  tube  at  a  point  about 
one-third  of  its  length  from  one  end.  A  narrow  strip  of  paper 
folded  into  a  shallow  trough  will  serve  as  a  boat  to  introduce  the 
powder  into  the  tube.  The  tube  is  then  inclined  at  as  sharp  an 
angle  as  possible,  with  the  mineral  lying  nearer  the  lower  end. 
The  tube  is  then  held  over  a  Bunsen  burner  flame  in  such  a  way 
that  the  flame  plays  on  the  upper  part  of  the  tube.  This  serves 
to  convert  the  inclined  tube  into  a  chimney,  up  which  a  current 
of  air  flows.  After  a  moment  the  tube  is  shifted  so  that  the  flame 


INSTRUMENTS,  REAGENTS,  ETC.  87 

heats  it  at  a  point  just  above  the  mineral,  or  in  some  cases  the 
flame  may  be  directly  beneath  the  mineral.  The  mineral  is 
being  heated  under  these  conditions  in  a  steady  current  of  air, 
and  it  will  be  oxidized  if  such  a  reaction  is  possible.  Various 
oxides  may  come  off  as  gases  and  either  escape  at  the  end  of  the 
tube  or  be  condensed  as  sublimates  upon  its  walls.  The  follow- 
ing table  gives  a  list  of  those  elements  which  yield  characteristic 
reactions  when  heated  in  open  tubes: 

Element.  Description  of  Test. 

Sulphur.  Sulphur  dioxide,  S02,  comes  out  of  upper  end  of  tube 
as  a  gas  with  a  pungent  and  irritating  odor.  If  a 
moistened  strip  of  blue  litmus  paper  is  placed  at  the 
upper  end  of  the  tube,  it  becomes  red,  due  to  the  acid 
reaction  caused  by  the  sulphurous  acid. 

Arsenic.  Arsenious  oxide,  As203,  condenses  at  a  considerable 
distance  above  the  heated  portion  as  a  volatile  coat- 
ing of  small  colorless  octahedral  crystals. 

Antimony.  Antimonious  oxide,  Sb203,  deposits  as  a  volatile 
white  ring  closer  to  the  heated  portion  of  the  tube 
than  the  arsenious  oxide.  Antimony  sulphides  yield 
also  a  dense  nonvolatile  white  sublimate  of  antimo- 
nate  of  antimony,  Sb204,  which  collects  along  the 
bottom  of  the  tube. 

Molybdenum.  Molybdenum  trioxide,  Mo03,  collects  near  the 
heated  portion  as  a  network  of  pale  yellow  to  white 
crystals. 

Mercury.  Collects  in  minute  gray  globules  which  can  be  rubbed 
together. 

Note.  Other  reactions  may  be  obtained  from  some  of  the 
above  elements  if  the  mineral  is  heated  too  rapidly  or  without 
the  establishment  of  a  strong  current  of  air  flowing  through  the 
tube. 

Closed  Tube  Test.  Frequently  a  small  glass  tube  which  has 
been  closed  at  one  end  is  useful  in  testing  minerals.  The  tube 


88  MANUAL  OF  MINERALOGY 

is  made  out  of  soft  glass  and  should  have  a  length  of  about 
3 1  inches  and  an  internal  diameter  from  £  to  T\  of  an  inch. 
Two  closed  tubes  can  easily  be  made  by  fusing  the  center  of  a 
piece  of  tubing  7  inches  in  length  and  pulling  it  apart.  The 
closed  tube  test  is  used  to  determine  what  takes  place  when  a 
mineral  is  subjected  to  heat  practically  out  of  contact  with  the 
air.  Ordinarily  there  is  no  chemical  reaction  involved.  In 
general,  in  the  closed  tube  the  mineral  will  break  down  into 
simpler  parts  if  that  is  possible,  but  otherwise  nothing  will  take 
place  except  possibly  a  fusion  of  the  mineral.  The  following 
table  gives  a  list  and  brief  description  of  the  important  closed 
tube  tests  : 

Substance.  Description  of  Test. 

Water,  H20.  All  minerals  containing  water  of  crystallization  or 
the  hydroxyl  radical  will  give  on  moderate  heating  a 
deposit  of  drops  of  water  on  the  cold  upper  walls  of 
the  tube. 

Sulphur,  S.  All  sulphides  which  contain  an  excess  of  sulphur 
will  give  a  sublimate  of  sulphur,  which  is  red  when 
hot  and  yellow  when  cold. 

Arsenic,  As.  Native  arsenic  and  some  arsenides  will  give  a 
deposit  of  metallic  arsenic.  This  consists  of  two 
rings,  one  being  composed  of  a  black  and  amorphous 
material,  the  other  lying  nearer  the  bottom  of  the 
tube,  of  a  silver-gray  and  crystalline  material. 

Oxysulphide  of  antimony,  Sb2S20.  Sulphide  of  antimony  and 
some  sulphantimonites  give  this  sublimate  in  the 
form  of  a  slight  coating  which  deposits  close  to  the 
bottom  of  the  tube.  It  is  black  when  hot  and  red 
when  cold.  It  is  accompanied  by  a  faint  deposit  of 
sulphur  further  up  the  tube. 

Sulphide  of  mercury,  HgS.  A  black  amorphous  sublimate  which 
forms  when  cinnabar  is  heated. 


INSTRUMENTS,  REAGENTS,  ETC. 


89 


Mercury,  Hg.  Gray  metallic  globules  of  metallic  mercury  are 
obtained  when  native  mercury  or  amalgams  are 
heated  or  when  the  sulphide  is  mixed  with  dry  sodium 
carbonate  and  heated. 

Flame  Test.  Certain  elements  may  be  volatilized  when 
minerals  containing  them  are  heated  intensely  before  the  blow- 
pipe and  so  impart  characteristic  colors  to  the  flame.  The 
flame  color  to  be  obtained  from  a  mineral  will  often  serve  as  an 
important  means  of  its  identification.  A  flame  test  may  be 
made  by  heating  a  small  fragment  of  the  mineral  held  in  the  for- 
ceps, but  a  more  decisive  test  is  usually  obtained  when  the  fine 
powder  of  the  mineral  is  introduced  into  the  Bunsen  burner 
flame  on  a  piece  of  fine  platinum  wire.  The  following  table  gives 
a  list  of  the  important  elements  which  yield  flame  colors.  It  is 
to  be  noted  that  a  mineral  may  contain  one  of  these  elements, 
but  because  of  the  nonvolatile  character  of  the  chemical  com- 
bination will  fail  to  give  a  flame  color. 


Element.       Color  of  Flame. 
Strontium.         Crimson. 


Lithium. 


Calcium. 


Sodium. 


Crimson. 


Orange. 


Intense  yellow. 


Remarks. 

Strontium  minerals  which  give 
the  flame  color  also  give  alka- 
line residues  after  being  heated. 
Lithium  minerals  which  give 
the  flame  color  do  not  give 
alkaline  residues  after  being 
heated. 

In  the  majority  of  cases  a  dis- 
tinct calcium  flame  will  be  ob- 
tained only  after  the  mineral 
has  been  moistened  with  HC1. 
A  very  delicate  reaction.  The 
flame  should  be  very  strong 
and  persistent  to  indicate  the 
presence  of  sodium  in  the  min- 
eral as  an  essential  constit- 
uent. 


90 


MANUAL  OF  MINERALOGY 


Element.        Color  of  Flame. 

Barium.  Yellow  green. 

Molybdenum.    Yellow  green. 
Boron.  Yellow  green. 

f  Emerald-green. 

Copper.          \ 

Azure-blue. 


Zinc. 


Lead. 


Bluish  green. 


Pale  azure-blue. 


Remarks. 

Minerals  which  give  the  barium 
flame  also  give  alkaline  resi- 
dues after  ignition. 

Obtained  from  the  oxide  or  sul- 
phide of  molybdenum. 

Minerals  giving  a  boron  flame 
rarely  give  alkaline  residues 
after  ignition. 

Obtained   from   the  oxide   of 

copper. 

Obtained  from  the  chloride  of 

copper. 

Appears  usually  as  bright 
streaks  and  threads  in  the 
flame. 

Tinged  with  green  in  the  outer 
parts. 


Color  Reactions  with  the  Fluxes.  Some  elements,  when 
dissolved  in  certain  fluxes,  give  a  characteristic  color  to  the 
fused  mass.  The  fluxes  that  are  most  commonly  used  are  borax, 
Na2B407.10H20,  sodium  carbonate,  Na2C03,  and  salt  of  phos- 
phorus, HNaNH4P04.4H20.  The  operation  is  best  performed  by 
first  fusing  the  flux  on  a  small  loop  of  platinum 
wire  into  the  form  of  a  lens-shaped  bead.  The 
loop  on  the  wire  should  best  have  the  shape  and 
size  shown  in  Fig.  202.  After  the  flux  has  been 
fused  into  a  bead  on  the  wire,  a  small  amount  of 
the  powdered  mineral  is  introduced  into  it  and  is 
Fig.  202.  Loop  dissolved  by  further  heating.  The  color  of  the 

of     Platinum  .  i .         .         .  ,  ,  .     , . 

wire  for  Bead  resulting  bead  may  depend  upon  whether  it  was 
.    heated  in  the   oxidizing   or  reducing  flame  and 


whether  the  bead  is  hot  or  cold, 
list  of  the  important  bead  tests : 


The  following  table  gives  a 


INSTRUMENTS,  REAGENTS,  ETC. 


91 


Table  of  Color  Reactions  with  the  Fluxes. 


Oxides  of 

Borax  Bead. 

Phosphorus  Salt  Bead. 

Oxidizing  flame. 

Reducing 
flame. 

Oxidizing  flame 

Reducing 
flame. 

Chromium. 

Hot. 

Yellow. 

Green. 

Dirty  green. 

Dirty  green. 

Cold. 

Yellowish  green. 

Green. 

Fine  green. 

Fine  green. 

Vanadium. 

Hot. 

Yellow. 

Dirty  green. 

Yellow. 

Dirty  green. 

Cold. 

Yellowish  green 
almost    color- 
less. 

Fine  green. 

Yellow. 

Fine  green. 

Uranium. 

Hot. 

Deep  yellow  to 
orange-red. 

Pale  green. 

Yellow. 

Pale  dirty 
green. 

Cold. 

Yellow. 

Pale  green  to 
nearly  colorless. 

Pale  greenish 
yellow. 

Fine  green. 

Iron. 

Hot. 

Deep  yellow  to 
orange-red. 

Bottle-green. 

Deep  yellow  to 
brownish  red. 

Red-yellow 
to  yellow- 
green. 

Cold. 

Yellow. 

Pale  bottle- 
green. 

Yellow  to  al- 
most colorless. 

Almost  color- 
less. 

Copper. 

Hot. 

Green. 

Colorless  to 
green. 

Green. 

Brownish 
green. 

Cold. 

Blue. 

Opaque  red 
with  much 
oxide. 

Blue. 

Opaque  red. 

Cobalt. 

Hot. 

Blue. 

Blue. 

Blue. 

Blue. 

Cold. 

Blue. 

Blue. 

Blue. 

Blue. 

Nickel. 

Hot. 

Violet. 

Opaque  gray. 

Reddish  to 
brownish  red. 

Reddish  to 
brownish 
red. 

Cold. 

Reddish  brown. 

Opaque  gray. 

Yellow  to  red- 
dish yellow. 

Yellow  to  red- 
dish yellow. 

Manganese. 

Hot. 

Violet. 

Colorless. 

Grayish  violet. 

Colorless. 

Cold. 

Reddish  violet. 

Colorless. 

Violet. 

Colorless. 

Sodium  carbonate  with  oxide  of  manganese  gives  when  heated 
in  the  oxidizing  flame  an  opaque  bead,  green  when  hot,  bluish 


92  MANUAL  OF  MINERALOGY 

green  when  cold.    When  heated  in  the  reducing  flame  the  bead 
is  colorless. 

Dry  Reagents. 

The  following  paragraphs  give  a  brief  description  of  the  more 
important  dry  reagents  used  in  testing  minerals : 

Sodium  Carbonate,  Na2C03,  is  a  white  salt  that  is  used  chiefly 
as  a  flux  to  decompose  minerals  by  fusion  on  charcoal  and  more 
rarely  as  a  flux  in  a  bead  test. 

Borax,  Na2B407.10H20,  is  a  white  salt  that  is  used  chiefly  in 
making  bead  tests  and  more  rarely  as  a  flux  on  charcoal. 

Microcosmic  Salt  or  Salt  of  Phosphorus,  HNaNH4P04.4H20, 
is  a  white  salt  used  in  making  bead  tests. 

Acid  Potassium  Sulphate,  HKS04,  is  a  white  salt  that  is  used 
in  making  a  test  for  fluorine  (see  page  100). 

Acid  Potassium  Sulphate  and  Fluorite  Mixture  is  a  mixture 
of  three  parts  of  the  former  and  one  part  of  the  latter.  It  is  used 
in  making  a  test  for  boron  (see  page  97). 

Potassium  Iodide  and  Sulphur  Mixture.  A  mixture  of  equal 
parts  of  these  two  materials  is  used  in  making  a  test  for  bismuth 
(see  page  97). 

Tin  and  Zinc  are  used  in  granulated  form  to  make  certain  re- 
duction tests  in  hydrochloric  acid  solutions. 

Test  Papers.  Blue  litmus  paper  is  a  test  paper  which  changes 
in  color  from  blue  to  red  when  exposed  to  the  action  of  an  acid. 
It  is  most  commonly  used  in  the  open  tube  test  for  sulphur  (see 
page  109).  Yellow  turmeric  paper  is  a  test  paper  that  turns 
brown  when  exposed  to  the  action  of  an  alkali.  It  is  most 
commonly  used  in  making  a  test  for  the  presence  of  an  alkali 
or  alkaline  earth  in  a  mineral  (see  under  sodium,  page  109; 
calcium,  page  98,  etc.).  Red  litmus  paper  can  be  substituted 
for  the  yellow  turmeric.  It  turns  blue  when  exposed  to  the 
action  of  an  alkali. 

Wet  Reagents. 

The  following  paragraphs  give  a  brief  description  of  the  more 
important  wet  reagents  used  in  testing  minerals : 


TESTS   FOR  THE  ELEMENTS  93 

Hydrochloric  Acid,  Muriatic  Acid,  HC1,  is  an  acid  which  is 
commonly  used  for  the  solution  of  minerals,  etc.  It  is  a  non- 
oxidizing  acid.  The  ordinary  laboratory  acid  is  diluted  with 
three  parts  of  water. 

Nitric  Acid,  HN03,  is  a  strong  solvent  and  oxidizing  agent. 
It  is  commonly  used  in  its  concentrated  form. 

Sulphuric  Acid,  H2S04,  is  less  commonly  used  than  the  others 
as  a  solvent.  It  may  be  used  in  its  concentrated  form,  but 
usually  is  diluted  with  four  parts  of  water.  When  water  is  added 
to  the  acid  a  large  amount  of  heat  is  generated.  Water  should 
never  be  added  to  the  hot  acid.  The  acid  boils  at  337°  C. 

Ammonium  Hydroxide,  NH4OH,  is  a  strong  alkali  used 
chiefly  to  neutralize  acid  solutions  and  as  a  precipitant  for  alu- 
minium and  ferric  hydroxides  (see  pages  95  and  101).  For  labo- 
ratory use  it  is  commonly  diluted  with  three  parts  of  water. 

Ammonium  Carbonate,  (NH4)2C03,  and  Ammonium  Oxa- 
late,  (NH4)2C204,  are  chiefly  used  in  the  form  of  aqueous  solutions 
to  precipitate  the  alkaline  earths,  calcium,  strontium  and  barium, 
from  their  solutions  (see  page  98). 

Hydrogen  Sodium  Phosphate,  HNaaPCX,  is  used  in  the  form 
of  an  aqueous  solution  to  test  for  the  presence  of  magnesium 
(see  page  103);  Barium  Hydroxide,  Ba(OH)2,  in  testing  for  car- 
bon dioxide  (see  page  98) ;  Barium  Chloride,  BaCl2,  for  sulphu- 
ric acid  (see  page  110);  Ammonium  Molybdate,  (NH4)2Mo04, 
for  phosphoric  acid  (see  page  106);  Silver  Nitrate,  AgN03,  for 
chlorine  (see  page  99). 

Potassium  Ferrocyanide,  K4Fe(CN)6.3H20,  and  Potassium 
Ferricyanide,  K6Fe2(CN)i2,  are  used  in  dilute  solutions  to  test  for 
ferric  and  ferrous  iron  respectively  (see  page  102).  Ammonium 
Sulphocyanate,  NH4CNS,  is  also  used  to  test  for  ferric  iron. 
Cobalt  Nitrate,  Co(N03)2,  is  used  in  the  form  of  a  dilute  solution 
in  blowpipe  tests  for  aluminium  and  zinc  (see  pages  95  and  112). 

Tests  for  the  Elements. 

On  the  following  pages  will  be  given  brief  descriptions  of  the 
more  important  blowpipe  and  chemical  tests  for  the  elements 
as  they  occur  in  minerals.  In  order  to  facilitate  reference  to 


94 


MANUAL  OF  MINERALOGY 


this  section,  the  different  elements  will  be  treated  in  alphabetical 
order.  Under  each  element  the  tests  will  be  given  in  the  approxi- 
mate order  of  their  importance.  For  a  fuller  discussion  of  this 
part  of  the  subject  reference  must  necessarily  be  made  to  the 
textbooks  that  treat  of  it  alone.  Below  is  a  list  of  the  elements 
whose  tests  are  discussed,  with  their  chemical  symbols,  valence 
and  atomic  weights. 


Element. 

Sym- 
bol. 

Valence. 

Atomic 
Weight. 

Al 

Trivalent... 

27 

Sb 

Trivalent  and  pentavalent 

120 

\s 

75 

Ba 

Bivalent 

137 

Be 

g 

Bismuth         

Bi 

Trivalent 

208 

Boron     ' 

B 

Trivalent 

H 

Calcium         *.  .  . 

Ca 

Bivalent 

40 

c 

Tetravalent 

12 

Chlorine  

Cl 

Univalent  

35  5 

Cr 

52  5 

Cobalt        

Co 

Bivalent 

59 

Columbium,  see  Niobium. 
Copper     

Cu 

Univalent  and  bivalent 

63  4 

Fluorine                      .  . 

F 

Univalent 

19 

Glucinum,  see  Beryllium. 
Gold                 

Au 

197  3 

Hydrogen  

H 

Univalent 

1 

Fe 

Bivalent  and  trivalent 

56 

Lead 

Pb 

207 

Lithium        

Li 

Univalent 

7 

Me 

Bivalent 

24 

Manganese  

Mn 

Bivalent,  trivalent  and  tetravalent 

55 

Hg 

200 

Molybdenum  

Mo 

Tetravalent  and  sexivalent 

96 

Nickel                     

Ni 

59 

Niobium  

Nb 

Pentavalent     

94 

Oxygen               ... 

o 

Bivalent 

16 

Phosphorus  

P 

Pentavalent     

31 

Platinum  
Potassium  

Pt 
K 

Bivalent  and  tetravalent  
Univalent  

195 
39  1 

Silicon     

Si 

Tetravalent 

28 

Silver 

Ae 

108 

Sodium  

N! 

Univalent 

23 

Strontium 

Sr 

87  5 

Sulphur  

s 

Bivalent  and  sexivalent 

32 

Tantalum 

Ta 

182  6 

Tellurium.  .  . 

Te 

Bivalent. 

125 

Tin 

Sn 

119 

Titanium  
Tungsten  

Ti 
W 

Trivalent  and  tetravalent  
Sexivalent.         

48 
185 

Uranium   

u 

Tetravalent  and  sexivalent      .   . 

240 

Vanadium 

v 

51  4 

Zinc  

Zn 

Bivalent     

65  4 

ANTIMONY  95 


Aluminium. 

1.  Precipitation  by  Ammonium  Hydroxide.     Aluminium  is 
precipitated  in  the  form  of  aluminium  hydroxide,  A1(OH)3,  when 
an  excess  of  ammonium  hydroxide  is  added  to  an  acid  solution. 
The  precipitate  is  flocculent  in  form  and  colorless  or  white.   It  is 
precipitated  under  the  same  conditions  as  ferric  hydroxide  (see 
page  101),  and  since  the  latter  has  a  dark  color  a  small  amount 
of  aluminium  hydroxide  might  be  overlooked  in  a  mixture  of 
the  two.     To  make  a  further  test  under  these  conditions,  filter 
off  the  precipitate  and  treat  it  with  a  hot  solution  of  sodium 
hydroxide,  which  will  dissolve  any  aluminium  hydroxide  present 
but  will  not  affect  the  ferric  hydroxide.     Filter,  and  to  the  filtrate 
add  hydrochloric  acid  in  slight  excess,  and  then  make  alkaline 
with  ammonium  hydroxide  again.    This  will  precipitate  any 
aluminium  that  may  be  present  as  pure  aluminium  hydroxide. 

2.  Blowpipe  Test  with  Cobalt  Nitrate.     Light  colored  and 
infusible  aluminium  minerals  when  moistened  with  a  drop  of 
cobalt  nitrate  and  heated  intensely  before  the  blowpipe  assume 
a  dark  blue  color. 


Antimony. 

1.  Oxide  Coating  on  Charcoal.     When  an  antimony  mineral 
is  heated  in  the  oxidizing  flame  on  charcoal,  a  heavy  white  coat- 
ing of  antimony  oxide  settles  on  the  charcoal  at  a  short  distance 
from  the  mineral.    The  coating  is  readily  volatile  when  heated. 

2.  Open  Tube  Test.     When  metallic  antimony  or  a  compound 
of  antimony  with  sulphur  is  heated  in  the  open  tube,  a  white 
powdery  sublimate  of  antimony  oxide,  Sb203,  forms  in  a  ring 
on  the  inner  wall  of  the  tube,  a  short  distance  above  the  mineral. 
It  is  a  volatile  coating.     If  the  mineral  contains  sulphur,  as  is 
usually  the  case,  a  second  coating  will  form  as  a  white  powder 
along  the  bottom  of  the  tube.     It  is  another  oxide  of  antimony, 
Sb2C>4.     It  is  nonvolatile  and  is  usually  more  conspicuous  than 
the  first. 


96  MANUAL  OF  MINERALOGY 

Arsenic. 

The  test  to  be  used  for  arsenic  depends  upon  whether  the 
mineral  contains  oxygen.  In  the  majority  of  cases  an  arsenic 
compound  does  not  contain  oxygen,  and  then  tests  1,  2  and  3 
will  serve.  If,  on  the  other  hand,  the  mineral  is  an  oxygen  com- 
pound, test  4  must  be  used. 

1.  Oxide  Coating  on  Charcoal.     When  an  arsenic  mineral 
is  heated  in  the  oxidizing  flame  on  charcoal,  a  white  coating  of 
arsenious  oxide,  As203,  is  deposited  on  the  charcoal  at  some  dis- 
tance from  the  mineral.    The  coating  is  very  volatile.     Its  for- 
mation is  usually  accompanied  by  a  characteristic  odor  of  garlic. 

2.  Open  Tube  Test.     When  an  arsenic  mineral  is  carefully 
heated  in  the  open  tube  a  colorless  or  white  crystalline  sublimate 
of  arsenious  oxide,  As203,  forms  in  a  ring  on  the  inner  wall  of 
the  tube  at  a  considerable  distance  above  the  mineral.     It  is 
very  volatile.    When  examined  with  a  lens  the  coating  will 
usually  show  well-defined  octahedral  crystals.     If  the  mineral 
is  heated  too  rapidly,  metallic  arsenic  may  sublime  instead  of  the 
oxide  (see  the  next  test). 

3.  Closed  Tube  Test.     Many  arsenic  minerals  when  heated 
in  a  closed  tube  yield  a  sublimate  of  metallic  arsenic,  known  as 
the  arsenic  mirror.    This  sublimate  shows  an  amorphous  black 
band  above  and  a  silver-gray  crystalline  band  below.     If  the 
bottom  of  the  tube  be  broken  off  and  the  metallic  arsenic  volatil- 
ized by  heat,  the  characteristic  garlic  odor  will  be  obtained. 

4.  Closed  Tube  Test  for  an  Arsenate.     When  arsenic  occurs 
in  a  mineral  in  the  form  of  an  arsenate,  i.e.,  an  oxidized  com- 
pound, none  of  the  above  tests  will  serve.    In  this  case  place  the 
mineral  in  a  closed  tube  with  a  splinter  of  charcoal  and  then 
heat.    The  charcoal  will  act  as  a  reducing  agent  and  set  metallic 
arsenic  free,  which  will  condense  on  the  wall  of  the  tube  as  an 
arsenical  mirror  similar 'to  that  described  under  test  3. 

Barium. 

1.  Flame  Test.  Barium  minerals  when  heated  intensely  give 
a  yellowish  green  flame  color. 


BORON  97 

2.  Precipitation  as  Barium  Sulphate.     Barium  is  precipi- 
tated as  barium  sulphate,  BaS04,  from  an  acid  solution  by  the 
addition  of  dilute  sulphuric  acid.    The  precipitate  is  white  and 
finely  divided  and  being  very  insoluble  will  form  in  a  quite  dilute 
solution  (distinction  from  calcium  and  strontium). 

3.  Alkaline  Reaction.     Barium  is  an  alkaline  earth  metal. 
When  a  mineral  contains  barium  in  combination  with  a  volatile 
acid,  it  will  give,  after  ignition,  a  residue  which  will  react  alkaline 
on  a  piece  of  moistened  turmeric  paper. 

Beryllium  or  Glucinum. 

Beryllium  is  a  rare  element  which  has  no  simple  blowpipe  or 
chemical  test. 

Bismuth. 

1.  Charcoal  Tests.  When  heated  with  sodium  carbonate  on 
charcoal  in  the  reducing  flame,  a  bismuth  mineral  will  yield  a 
metallic  globule  and  an  oxide  coating.  The  metal  is  easily 
fusible,  lead-gray  when  hot,  but  becomes  covered  with  an  oxide 
coating  on  cooling.  It  is  only  imperfectly~malleable,  for  when 
hammered  out  it  flattens  at  first  but  later  breaks  into  small 
grains.  The  oxide  coating,  Bi203,  is  white  with  a  yellow  ring 
next  the  mineral.  These  bismuth  reactions  are  quite  similar  to 
those  for  lead  (see  page  102),  consequently  the  following  modi- 
fication is  useful.  If  the  bismuth  mineral  is  fused  on  charcoal 
with  a  mixture  of  potassium  iodide,  KI,  and  sulphur  (see  page 
92),  a  characteristic  and  distinctive  coating  is  obtained.  This 
sublimate  is  yellow  next  to  the  mineral  and  brilliant  red  on 
the  outside.  Under  similar  conditions  with  lead  a  solid  yellow 
coating  would  be  obtained. 

Boron. 

1.  Flame  Test.  Some  boron  minerals  give  a  yellow-green 
flame  when  heated  alone.  Most  boron  minerals,  however,  will 
only  yield  the  flame  color  when  their  powder  is  mixed  with  acid 
potassium  sulphate  and  fluorite  mixture  (see  page  92)  and  then 


98  MANUAL  OF  MINERALOGY 

introduced  on  a  platinum  wire  into  a  Bunsen  burner  flame.  As 
the  mixture  fuses,  a  momentary  but  distinct  green  flame  is 
obtained. 

Calcium. 

1.  Flame  Test.     When  calcium  occurs  in  a  mineral  in  such 
a  state  that  it  can  be  volatilized  by  heat,  it  will  yield  a  charac- 
teristic orange  flame  color.     Frequently  the  mineral  has  to  be 
moistened   by   hydrochloric   acid   before   heating.     The   flame 
should  not  be  confused  with  the  crimson  and  more  persistent 
flame  of  strontium  or  lithium. 

2.  Alkaline  Reaction.     Calcium   is   an   alkali-earth  metal. 
When  a  mineral  contains  calcium  in  a  combination  with  a  vola- 
tile acid,  it  will  give,  after  ignition,  a  residue  which  will  react 
alkaline  on  a  piece  of  moistened  turmeric  paper. 

3.  Precipitation  as  Calcium  Oxalate  or  Carbonate.     Cal- 
cium is  readily  and  completely  precipitated  from  alkaline  solu- 
tions as  calcium  oxalate,  CaC204,  or  calcium  carbonate,  CaC03, 
by  the  addition  of  ammonium  oxalate,  (NH4)2C204,  or  ammonium 
carbonate,  (NH4)2C03.     Both  precipitates  are  white  and  finely 
divided. 

4.  Precipitation  as  Calcium  Sulphate.     Calcium  is  precipi- 
tated from  a  concentrated  hydrochloric  acid  solution  as  calcium 
sulphate  on  the  addition  of  a  little  dilute  sulphuric  acid.    The 
precipitate  is  quite  readily  soluble  in  water  and  therefore  will 
not  form  in  a  dilute  solution   (distinction  from  barium  and 
strontium). 

Carbon. 

Carbon  exists  in  minerals  chiefly  in  the  form  of  carbonic  acid 
in  the  carbonates. 

1.  Test  for  Carbon  Dioxide  with  an  Acid.  All  carbonates 
when  treated  with  a  strong  acid  (best  hydrochloric)  dissolve 
with  a  vigorous  effervescence  of  carbon  dioxide  gas.  In  some 
cases  (for  example,  dolomite,  CaMg(C03)2)  the  acid  needs  to  be 
heated  to  start  the  reaction,  and  in  others  (for  example,  cerussite, 
PbC03)  a  dilute  acid  is  necessary.  Carbon  dioxide  gas  is  colorless 
and  odorless.  It  will  not  support  combustion,  as  is  shown  when 


COPPER  99 

a  lighted  match  is  placed  in  a  test  tube  that  contains  it.  The 
gas  is  heavier  than  air  and  can  be  poured  from  the  test  tube  in 
which  it  has  been  generated  into  another  in  which  some  barium 
hydroxide  solution  has  been  placed.  When  the  contents  of  the 
latter  tube  are  shaken  together,  the  carbon  dioxide  reacts  with 
the  barium  hydroxide  to  form  a  white  precipitate  of  barium 
carbonate,  BaC03. 

Chlorine. 

1.  Precipitation  as  Silver  Chloride.  Chlorine  is  precipi- 
tated from  a  dilute  nitric  acid  solution  as  silver  chloride,  AgCl, 
by  the  addition  of  a  small  amount  of  silver  nitrate,  AgN03. 
The  test  is  very  delicate,  traces  of  chlorine  being  shown  by  a 
milky  appearance  of  the  solution.  When  in  any  quantity  the 
precipitate  is  curdy  in  form.  It  is  white  on  precipitation  but 
darkens  on  exposure  to  light.  It  is  soluble  in  ammonium 
hydroxide. 

Chromium. 

1.  Bead  Tests.  Chromium  is  usually  tested  for  by  the  color 
it  gives  to  the  fluxes  (see  page  91).  The  salt  of  phosphorus  bead 
when  fused  in  the  oxidizing  flame  yields  a  fine  green  color.  This 
is  the  most  characteristic  chromium  bead. 

Cobalt. 

1.  Bead  Tests.  A  cobalt  mineral  when  fused  in  either  a 
borax  or  salt  of  phosphorus  bead  yields  a  distinctive  dark  blue 
color.  The  test  is  very  delicate. 

Columbium,  see  Niobium. 

Copper. 

1.  Flame  Tests.  An  oxidized  compound  of  copper  when 
introduced  into  the  flame  gives  it  a  vivid  green  flame  color  due 
to  the  copper  oxide  volatilized.  When  the  mineral  is  moistened 
with  hydrochloric  acid  and  then  heated,  the  flame  color  is  an 
intense  blue.  If  the  mineral  is  a  sulphide,  it  must  be  roasted  in 
the  oxidizing  flame  before  moistening  with  hydrochloric  acid. 


100  MANUAL  OF  MINERALOGY 

2.  Blue  Solution  with  Ammonium  Hydroxide.     If  an  acid 
solution  containing  copper  is  made  alkaline  with  ammonium 
hydroxide,  it  will  assume  a  deep  blue  color. 

3.  Reduction    to    Metal    on    Charcoal.     When    a    small 
amount  of  a  copper  mineral  is  mixed  with  a  flux  (best  equal 
parts  of  sodium  carbonate  and  borax),  placed  on  charcoal  and 
heated  intensely  in  the  reducing  flame,  metallic  globules  of  cop- 
per will  be  formed.    They  are  difficultly  fusible,  bright  when 
hot,  but  become  coated  with  an  oxide  coating  on  cooling.     They 
are  malleable  and  show  the  characteristic  copper  color.     Sul- 
phides of  copper  must  first  be  roasted  in  the  oxidizing  flame  in 
order  to  remove  the  sulphur  before  mixing  with  the  flux. 

Fluorine. 

1.  Etching  Tests.  The  ordinary  test  for  fluorine  consists 
in  converting  it  into  hydrofluoric  acid  and  observing  the  latter's 
etching  effect  upon  glass.  A  watch  glass  or  other  piece  of  glass 
may  be  covered  with  paraffin  and  then  the  coating  removed 
in  spots.  Upon  this  is  placed  the  powdered  mineral  with  a 
few  drops  of  concentrated  sulphuric  acid.  The  action  of  the 
acid  upon  the  fluoride  will  serve  to  liberate  hydrofluoric  acid, 
which  will  in  turn  etch  the  glass  where  it  has  been  exposed. 
The  action  should  be  allowed  to  continue  for  some  time,  when 
on  cleaning  the  glass  the  etched  spots  will  be  visible. 

A  modification  of  the  above  test  can  be  made  in  a  closed  tube. 
Take  a  closed  tube  of  about  j  inch  diameter  and  made  preferably 
of  hard  glass.  Into  this  introduce  a  powdered  mixture  of  the 
mineral,  glass  and  acid  potassium  sulphate,  and  then  heat  in 
the  Bunsen  burner  flame.  When  heated,  acid  potassium  sul- 
phate is  converted  into  the  normal  -potassium  sulphate  with 
the  liberation  of  sulphuric  acid.  The  acid  attacks  the  fluoride 
and  sets  free  hydrofluoric  acid.  This  in  turn  acts  upon  the  glass 
present  and  etches  it.  The  etching,  however,  is  not  readily 
apparent  on  account  of  the  conditions  of  the  experiment.  As  a 
secondary  reaction,  however,  there  will  be  formed  in  the  upper 
part  of  the  tube  a  white  sublimate  of  silicon  dioxide.  This 
sublimate  is  volatile  because  of  the  presence  with  it  of  small 


IRON      '  101 

amounts  of  hydrofluosilicic  acid.  If  the  bottom  of  the  tube  is 
broken  off  and  its  interior  gently  washed  with  water,  this  acid 
will  be  dissolved  and  removed.  If  the  tube  is  now  dried  again, 
the  white  coating  will  prove  to  be  no  longer  volatile.  This 
silicon  dioxide  coating  is  a  proof  of  the  action  of  hydrofluoric 
acid  in  the  bottom  of  the  tube  and  therefore  of  the  presence 
of  fluorine  in  the  mineral. 

Glucinum,  see  Beryllium. 

Gold. 

There  is  no  simple  blowpipe  or  chemical  test  for  gold.  Or- 
dinarily its  physical  characteristics  are  sufficient  to  identify  it. 
For  a  discussion  of  the  occurrence  and  tests  for  gold  see  page  126. 

Hydrogen. 

1.  Closed  Tube  Test  for  Water.  Hydrogen  exists  in  min- 
erals either  as  water  of  crystallization  (for  example,  gypsum, 
CaS04.2H20)  or  as  the  hydroxyl  radical  (for  example,  brucite, 
Mg(OH)2).  In  either  case  its  presence  may  be  detected  by 
heating  a  fragment  of  the  mineral  in  a  closed  tube  and  observing 
the  water  which  condenses  upon  the  upper  cold  wall  of  the  tube. 
Water  of  crystallization  is  driven  off  more  readily  than  water  of 
hydroxyl,  but  the  test  is  easily  obtained  in  either  case. 

Iron. 

1.  Magnetic  Test.     Any  mineral  that  contains  a  sufficient 
amount  of  iron  to  permit  it  to  be  classified  as  an  iron  mineral 
will  readily  become  magnetic  when  heated  in  the  reducing  part 
of  the  blowpipe  flame.     A  comparatively  small  fragment  should 
be  used  and  the  test  made  with  a  magnet  after  it  has  cooled. 

2.  Precipitation  with  Ammonium  Hydroxide.     Ferric  iron 
is   readily   and   completely   precipitated   as   ferric   hydroxide, 
Fe(OH)3,  from  an  acid  solution  by  adding  an  excess  of  ammo- 
nium hydroxide.     It  is  a  flocculent  precipitate  with  a  reddish 


102  'MANUAL  OF  MINERALOGY 

brown  color.  If  there  is  any  doubt  as  to  the  state  of  oxidation 
of  the  iron  in  the  original  solution,  a  few  drops  of  nitric  acid 
should  be  added  and  the  solution  heated  in  order  to  make  cer- 
tain that  the  iron  is  ferric. 

3.  Cyanide  Tests  for  Ferrous  and  Ferric  Iron.  Occa- 
sionally it  may  be  important  to  determine  whether  the  iron  in 
a  mineral  is  ferrous  or  ferric  in  its  valence.  This  can  be  done 
only  when  the  mineral  is  soluble  in  a  nonoxidizing  acid  like 
hydrochloric  and  when  it  is  not  a  sulphide.  If  these  conditions 
can  be  fulfilled,  then  divide  the  solution  into  two  parts.  To  one 
add  a  few  drops  of  a  dilute  solution  of  potassium  /m'cyanide, 
and  if  the  solution  contains  any  ferrous  iron  a  heavy  dark  blue 
precipitate  will  form.  If,  on  the  other  hand,  it  contained  only 
ferric  iron,  there  would  be  no  precipitate  but  only  a  darkening 
of  the  color  of  the  solution.  To  the  second  portion  of  the 
solution  add  a  few  drops  of  a  dilute  solution  of  potassium  fero- 
cyanide,  and  if  there  is  any  ferric  iron  present  a  heavy  dark  blue 
precipitate  similar  to  the  one  in  the  previous  case  will  form. 
But  if  the  solution  contained  only  ferrous  iron,  a  light  blue 
precipitate  would  be  formed.  The  characteristic  dark  blue  pre- 
cipitate must  contain  both  valences  of  iron  and  will  only  form 
when  a  cyanide  is  added  containing  the  opposite  kind  of  iron  to 
that  already  in  the  solution. 

Ammonium  or  potassium  sulphocyanate  is  also  used  in  making 
the  ferric  test.  A  few  drops  of  one  of  these  reagents  added  to 
a  ferric  iron  solution  will  give  it  a  deep  red  color.  All  of  these 
tests  are  extremely  delicate  and  will  give  good  results  if  only  a 
trace  of  iron  is  present.  They  should  never  be  used  to  deter- 
mine the  presence  of  iron  in  a  mineral  but  only  to  differentiate 
ferrous  from  ferric  iron. 

Lead. 

1.  Charcoal  Test.  Any  lead  mineral  when  powdered  and 
mixed  with  sodium  carbonate  will  yield  a  metallic  globule  when 
the  mixture  is  heated  on  charcoal  in  the  reducing  flame.  The 
globule  is  bright  lead  color  when  hot,  but  becomes  covered  with 
a  dull  oxide  coating  on  cooling.  It  is  very  malleable  and  can 


MAGNESIUM  103 

be  hammered  out  into  a  thin  sheet.  A  coating  on  the  charcoal 
of  lead  oxide,  PbO,  will  also  form,  which  varies  in  color  from 
yellow  next  to  the  fused  mass  to  white  at  a  distance.  It  will  be 
best  obtained  by  removing  the  lead  globule  to  a  fresh  piece  of 
charcoal  and  heating  it  in  the  oxidizing  flame. 

2.  Acid  Tests.  Lead  minerals  as  a  rule  are  only  slowly 
attacked  by  acids.  Dilute  nitric  acid  is  the  best  solvent  to  use. 
If  to  a  nitric  acid  solution  a  few  drops  of  hydrochloric  or  sul- 
phuric acid  are  added,  white  precipitates  will  form,  which  are 
respectively  lead  chloride,  PbCl2,  and  lead  sulphate,  PbS04. 
The  latter  is  quite  insoluble. 

Lithium. 

1.  Flame  Test.  Lithium  is  a  rare  element  which  is  to  be 
distinguished  by  the  persistent  and  strong  crimson  color  which 
it  gives  to  the  flame. 

Magnesium. 

1.  Precipitation  as  Ammonium  Magnesium  Phosphate. 
The  only  common  test  for  magnesium  is  to  precipitate  it  in  the 
form  of  ammonium  magnesium  phosphate,  NH4MgP04,  by  the 
addition  of  hydrogen  sodium  phosphate,  HNa2P04,  to  a  strongly 
ammoniacal  solution.  The  precipitate  usually  forms  somewhat 
slowly,  is  white  in  color  and  frequently  is  granular  in  texture. 
In  order  to  make  a  decisive  test  certain  precautions  are  neces- 
sary. As  the  precipitation  is  made  in  an  ammoniacal  solution, 
any  precipitates  formed  by  an  excess  of  ammonium  hydroxide 
must  be  first  filtered  off.  It  may  be  necessary  before  adding 
the  ammonium  hydroxide  to  add  a  few  drops  of  nitric  acid  so 
as  to  make  certain  that  any  iron  in  the  solution  is  in  the  ferric 
state.  •  Also,  before  making  the  final  test,  any  elements,  such 
as  calcium,  strontium  and  barium,  that  are  precipitated  in  am- 
moniacal solution  by  means  of  ammonium  oxalate,  must  be 
removed.  In  any  case  their  presence  must  be  tested  for  before 
adding  the  hydrogen  sodium  phosphate,  because,  if  present,  they 
would  be  precipitated  by  that  reagent  along  with  the  magnesium. 


104  MANUAL  OF  MINERALOGY 

Manganese. 

1.  Bead  Tests,  a.  Manganese  gives  to  the  sodium  carbo- 
nate bead  when  heated  in  the  oxidizing  flame  a  characteristic 
bluish  green  color.  The  bead  is  opaque  when  cold. 

b.  With  the  borax  bead,  when  heated  in  the  oxidizing  flame 
manganese  gives  a  purple  or  amethystine  color.  The  bead  is 
transparent  when  cold. 

Both  tests  are  very  delicate. 

Mercury. 

1.  Closed  Tube  Tests.     The  powdered  mineral  is  thoroughly 
mixed  with  dry  sodium  carbonate  and  placed  in  a  closed  tube 
and  then  heated.     The  sodium  carbonate  will  decompose  the 
mineral  and  liberate  metallic  mercury,  which  will  volatilize  and 
condense  in  the  upper  part  of  the  tube. 

2.  Precipitation  on   Copper.      Boil  the  powdered  mineral 
with  hydrochloric  acid,  into  which  some  powdered  pyrolusite, 
Mn02,  has  been  placed.    The  chlorine  evolved  by  the  action 
of  the  acid  on  the  manganese  dioxide  will  serve  to  dissolve  the 
mercury  mineral.     If  into  this  solution  a  clean  strip  of  copper 
is  placed  (a  cent  which  has  been  cleaned  with  a  little  nitric  acid 
will  serve),  it  will  become  covered  by  a  thin  coating  of  metallic 
mercury. 

The  chief  and  only  common  mineral  of  mercury  is  cinnabar, 
HgS,  and  for  its  distinctive  physical  and  chemical  tests  see 
•page  145. 

Molybdenum. 

The  tests  for  the  rare  element  molybdenum  depend  upon 
whether  it  is  in  combination  with  sulphur  or  in  an  oxygen  com- 
pound. See  under  molybdenite,  page  137,  and  under  wulfenite, 
page  308,  for  descriptions  of  the  various  tests. 

Nickel. 

1.  Borax  Bead  Test.  When  dissolved  in  a  borax  bead  in  the 
oxidizing  flame,  nickel  will  give  it  a  brownish  color.  If  the  bead 
is  heated  in  the  reducing  flame  for  some  time,  it  will  become 


OXYGEN  105 

opaque  because  of  the  separation  in  it  of  metallic  nickel.  The 
brown  color  due  to  nickel  is  often  masked  by  the  deep  blue  color 
due  to  the  presence  of  cobalt,  which  is  frequently  associated 
with  nickel  in  its  occurrence.  In  this  case  there  is  no  simple 
test  for  nickel. 

2.  In  Ammoniacal  Solution.  A  comparatively  strong  acid 
solution  of  nickel  will  on  the  addition  of  an  excess  of  ammonium 
hydroxide  become  light  blue  in  color.  The  test  should  not  be 
confused  with  the  similar  but  stronger  test  for  copper. 

Niobium. 

Niobium,  or  columbium,  as  it  is  sometimes  called,  is  a  rare 
acid  element  that  is  associated  with  tantalum  in  the  niobates 
and  tantalates. 

1.  Reduction  Test  with  Tin.  The  best  test  for  niobium 
is  to  fuse  some  of  the  powdered  mineral  with  several  parts  of 
sodium  carbonate.  The  resulting  mass  is  dissolved  in  a  few 
cubic  centimeters  of  dilute  hydrochloric  acid  and  then  a  few 
grains  of  metallic  tin  are  added.  The  solution  is  boiled  and  the 
hydrogen  set  free  by  the  action  of  the  acid  on  the  tin  serves  as 
a  reducing  agent.  The  result  is  to  form  a  compound  of  niobium 
which  is  dark  blue  in  color.  This  color  does  not  readily  change 
to  brown  on  continued  boiling,  and  disappears  on  addition  of 
water.  This  distinguishes  the  niobium  test  from  a  similar  one 
for  tungsten  (see  page  111). 

Oxygen. 

While  oxygen  is  one  of  the  most  common  elements  in  minerals, 
its  presence  is  ordinarily  determined  indirectly  by  testing  for 
the  different  oxygen  acids.  In  the  case  of  a  few  oxides  in  which 
there  is  an  excess  of  oxygen,  a  direct  test  may  be  made. 

1.  Closed  Tube  Test.  The  powdered  oxide  is  placed  in  a 
closed  tube  with  a  small  splinter  of  charcoal  resting  just  above 
it.  The  tube  is  heated  and  if  free  oxygen  is  evolved  the  charcoal 
will  at  first  glow  and  then  burn  with  a  bright  light.  It  is  to  be 
noted  that  only  a  few  oxides  which  contain  an  excess  of  oxygen 
will  give  this  test. 


106  MANUAL  OF  MINERALOGY 

Phosphorus. 

1.  Precipitation  with  Ammonium  Molybdate.     Phosphorus 
exists  in  minerals  in  the  form  of  phosphoric  acid  in  the  phos- 
phates.    It  is  best  tested  for  by  forming  a  dilute  nitric  acid 
solution  of  the  mineral  and  adding  a  few  cubic  centimeters  of 
this  to  an  excess  of  ammonium  molybdate  solution.     A  canary- 
yellow  precipitate    of   ammonium   phosphomolybdate  will   be 
formed.     The  precipitate  forms  slowly  at  first  and  comes  down 
best  in  a  warm  solution. 

2.  Flame  Test.     Many  phosphates  when  heated  before  the 
blowpipe  give  a  pale  bluish  green  flame  color.     This  may  fre- 
quently be  obtained  better  when  the  mineral  has  previously 
been  moistened  with  a  drop  of  concentrated  sulphuric  acid. 

Platinum. 

There  are  no  simple  blowpipe  or  chemical  tests  for  platinum. 
The  physical  characteristics  of  the  metal  are  usually  sufficient 
for  its  identification  (see  page  132). 

Potassium. 

1.  Flame  Test.  Volatile  potassium  salts  give  a  character- 
istic pale  violet  flame  color.  The  potassium  flame  will,  how- 
ever, commonly  be  obscured  by  the  stronger  yellow  flame  of 
sodium.  This  difficulty  can  be  overcome  by  filtering  the  flame 
through  a  piece  of  blue  glass.  The  sodium  flame,  being  a  mono- 
chromatic light,  cannot  pass  through  the  blue  glass,  while  the 
violet  flame  of  potassium  will  be  visible. 

When  the  potassium  does  not  exist  in  the  mineral  in  a  volatile 
state,  as  in  the  case  with  potassium  silicates,  the  powdered  min- 
eral must  be  first  thoroughly  mixed  with  gypsum  (CaS04.2H20) 
and  the  mixture  introduced  into  the  Bunsen  burner  flame  on 
a  platinum  wire.  There  will  be  a  reaction  between  the  two, 
and  the  potassium  will  be  liberated  in  the  form  of  a  sulphate, 
which,  being  a  volatile  salt,  will  give  the  flame  color.  It  will 
be  momentary  in  duration  and  must  be  viewed  through  the 
blue  glass. 


SILICON  107 

Silicon. 

Silicon  exists  as  the  acid  element  in  the  large  group  of  minerals 
known  as  the  silicates.  Some  of  these  are  readily  soluble  in 
acids,  but  the  greater  part  are  quite  insoluble.  The  tests  em- 
ployed differ  somewhat  in  the  two  cases.  • .-\- 

1.  Test  for  a  Soluble  Silicate.     If  the  silicate  is  soluble,  it 
should  be  powdered  and  dissolved  in  boiling  hydrochloric  acid. 
When  this  solution  is  evaporated  a  jellylike  material  will  sepa- 
rate out  just  before  dryness  is  reached.     This  silica  jelly,  as 
it  is  called,  is  a  form  of  silicic  acid  and  proves  the  presence  of 
silicon  in  the  mineral.     On  continued  evaporation  it  will  be 
dehydrated  and  converted  into  a  sandy  and  insoluble  substance 
having  the  composition  of  silicon  dioxide,  Si02. 

2.  Test  for  an  Insoluble  Silicate.     In  the  case  of  an  in- 
soluble silicate,  the  mineral  must  be  decomposed  by  fusion 
with  sodium  carbonate  before  treating  it  with  an  acid.     Make 
a  mixture  of  one  part  of  the  powdered  mineral  to  three  parts  of 
sodium  carbonate  and  fuse  thoroughly  before  the  blowpipe  on  a 
loop  of  platinum  wire.    It  is  best  to  make  two  or  three  such 
beads.    The  fusion  serves   to  decompose  the  silicate  and  to 
render  the  resulting  mass  wholly  soluble  in  acids.    The  beads 
are  powdered  and  dissolved  in  boiling  dilute  nitric  acid.    The 
evaporation  is  conducted  as  explained  in  experiment  1  and  a 
similar  silica  jelly  is  obtained. 

Frequently  it  is  desirable  to  make  tests  for  the  bases  which 
are  present  in  the  silicate.  In  this  case,  after  the  formation  of 
the  jelly,  continue  the  evaporation  to  complete  dryness.  This 
converts  the  silicon  into  the  insoluble  oxide  but  leaves  the  bases 
in  the  form  of  various  soluble  salts.  Treat  the  residue  in  the 
test  tube  with  a  little  water  and  hydrochloric  acid,  warm  and 
filter  from  the  insoluble  silica.  Add  an  excess  of  ammonium 
hydroxide  to  the  filtrate  to  precipitate  any  aluminium  or  ferric 
iron  as  their  respective  hydroxides.  Filter  if  necessary,  and  to 
the  filtrate  add  a  little  ammonium  oxalate  to  precipitate  any 
calcium  as  calcium  oxalate.  Filter  again,  and  to  the  filtrate  add 
more  ammonium  hydroxide  if  necessary  and  then  a  little  hydro- 


108  MANUAL  OF  MINERALOGY 

gen  sodium  phosphate,  which  will  precipitate  any  magnesium 
present  as  ammonium  magnesium  phosphate. 

3.  Decomposition  of  Silicates  by  Acids.     Certain  silicates, 
when  their  powder  is  treated  with  boiling  hydrochloric  acid, 
are  decomposed,  the  bases  going  into  solution  and  the  silicon 
separating  as  the  dioxide,  Si02.     In  this  case  there  would  be 
no  jelly  formed  when  the  solution  is  evaporated.     The  mineral 
powder  in  such  cases  disappears,  but  the  solution  never  becomes 
perfectly  clear  owing  to  the  silica,  which  remains  in  suspension 
in  the  solution.     It  gives  the  solution  a  translucent  appearance. 
The  surest  proof  that  the  mineral  has  been  decomposed  is  to 
filter  the  solution  and  test  for  various  bases  in  the  filtrate  in  a 
similar  manner  to  that  described  under  test  2. 

4.  Test  with  the   Salt   of  Phosphorus   Bead.     When  the 
powder  of  a  silicate  is  heated  in  a  salt  of  phosphorus  bead,  the 
bases  are  dissolved,  leaving  the  silica  present  as  an  insoluble 
translucent  skeleton. 

Silver. 

1.  Reduction  to  the  Metal  on  Charcoal.     Silver  can  fre- 
quently be  reduced  to  a  metallic  globule  from  its  compounds 
by  heating  the  powdered  mineral  on  charcoal  with  sodium  car- 
bonate.    The  resulting  globule  is  bright  both  when  hot  and 
cold.     It   is  malleable.     No  accompanying  coating  is  formed 
on  the  charcoal.     This  test  for  silver  is  frequently  complicated 
by  the  presence  of  lead,  arsenic  or  antimony  in  the  mineral. 
Usually  the  mineral  should  be  carefully  roasted  on  charcoal  in 
the  oxidizing  flame  before  attempting  the  reduction  in  order  to 
remove  the  last  two;  otherwise  a  brittle  globule  will  result. 
In  many  cases  the  only  satisfactory  test  for  silver  is  the  fire 
assay. 

2.  Precipitation  as  Silver  Chloride.     When  a  silver  mineral 
is  dissolved  in  nitric  acid  and  to  the  solution  a  few  drops  of 
hydrochloric  acid  is  added,  a  white  curdy  precipitate  of  silver 
chloride,  AgCl,  is  formed.    The  test  is  quite  delicate,  and  if 
there  is  only  a  trace  of  silver  in  the  solution  its  presence  will  be 
indicated  by  a  milky-blue  coloration.     The  precipitate  is  white 


SULPHUR  109 

at  first  but  darkens  on  exposure  to  light.  It  is  soluble  in  am- 
monium hydroxide.  Frequently  when  a  silver  mineral  is  treated 
with  nitric  acid  a  precipitate  will  result  at  once.  This  may  be 
metantimonic  acid,  lead  sulphate,  etc.,  and  should  be  filtered 
off  before  making  the  silver  test. 

Sodium. 

1.  Flame  Test.  Sodium  compounds  when  heated  give  a 
strong  and  persistent  yellow  flame.  The  test  is  very  delicate 
and  must  be  used  with  care,  for  only  a  trace  of  sodium  may 
yield  a  distinct  flame.  If  the  mineral  contains  sodium  in  any 
notable  amount,  it  should  give  an  intense  and  continuous  flame 
color. 

Strontium. 

1.  Flame  Color.     Strontium  compounds  give  a  very  strong 
and  persistent  crimson  flame.     The  only  other  flame  which  is 
similar  is  that  obtained  from  lithium.     Strontium  can  be  posi- 
tively determined  from  lithium  by  the  following  tests. 

2.  Alkaline  Reaction.     When  a  mineral  contains  strontium 
in  combination  with  a  volatile  acid,  it  will  give,  after  ignition,  a 
residue  which  will  react  alkaline  on  a  piece  of  moistened  turmeric 
paper. 

3.  Precipitation  as  Strontium  Sulphate.     Strontium  is  pre- 
cipitated from  a  mediumly  dilute  solution  as  strontium  sulphate, 
SrS04,  on  the  addition  of -a  little  dilute  sulphuric  acid.    The 
precipitate  is  somewhat  soluble  and  will  not  form  in  very  dilute 
solutions  (distinction  from  calcium  and  barium,  which  see). 

Sulphur. 

Sulphur  exists  in  minerals  either  without  oxygen,  as  in  the 
sulphides,  or  with  oxygen,  as  in  the  sulphates.  These  two  types 
of  sulphur  compounds  require  different  tests. 

Tests  for  Sulphur  in  Sulphides. 

1.  Open  Tube  Test.  Sulphides  when  heated  in  the  open 
tube  give  off  sulphur  dioxide  gas,  which  escapes  with  the  current 


HO  MANUAL  OF  MINERALOGY 

of  air  from  the  upper  end  of  the  tube.  Its  presence  can  be  de- 
tected by  its  pungent  and  irritating  odor.  A  piece  of  moistened 
blue  litmus  paper  inserted  into  the  upper  end  of  the  tube  will 
turn  red  on  account  of  the  sulphurous  acid  formed. 

2.  Charcoal   Test.      The  odor  of  sulphur  dioxide  may  be 
obtained  when  a  sulphide  is  roasted  on  charcoal. 

3.  Fusion  with   Sodium   Carbonate.     When  a  sulphide  is 
fused  on  charcoal  with  sodium  carbonate,  the  residue,  unless  the 
heating  has  been  too  prolonged,  will  contain  sodium  sulphide. 
If  the  slag  is  removed  and  placed  with  a  drop  of  water  on  a 
clean  silver  surface  (a  coin  will  serve),  there  will  result  a  dark 
brown  stain  due  to  the  formation  of  silver  sulphide. 

Tests  for  Sulphur  in  Sulphates. 

The  test  for  sulphuric  acid  depends  upon  whether  the  sulphate 
is  soluble  or  insoluble  in  acids. 

1.  Test  for  a  Soluble  Sulphate.     If  the  sulphate  is  soluble, 
treat  it  with  hydrochloric  acid,  and  to  the  resulting  solution  add 
a  little  barium  chloride.    A  heavy  white  precipitate  of  barium 
sulphate  will  result. 

2.  Test  for  an  Insoluble  Sulphate.     Powder  the  mineral, 
mix  with  sodium  carbonate  and  charcoal  dust  and  fuse  on  char- 
coal in  the  reducing  flame.    The  charcoal  serves  to  reduce  the 
sulphate  to  a  sulphide,  so  that  the  resulting  slag  contains  sodium 
sulphide.    When  the  fused  mass  is  placed  with  a  drop  of  water 
on  a  clean  silver  surface,  a  dark  brown  stain  of  silver  sulphide 
will  form.    It  is  to  be  noted  that  a  sulphide  would  yield  the 
same  test  (see  above) ,  so  that  it  is  necessary  to  make  certain  that 
the  mineral  being  tested  does  not  belong  to  that  chemical  group. 

Tantalum. 

There  is  no  simple  test  for  tantalum.     It  is  usually  associated, 
however,  with  niobium  (see  page  105). 

Tellurium. 

1.  Test  with  Sulphuric  Acid.     When  a  telluride  is  heated 
in  concentrated  sulphuric  acid,  it  gives  a  deep  crimson  color  to 


TUNGSTEN  111 

the  solution.     The  color  will  disappear  if  the  acid  is  heated  too 
hot,  or  if  after  cooling  it  is  diluted  with  water. 

2.  Charcoal  Test.  When  heated  on  charcoal  a  white  sub- 
limate of  TeO2  is  formed  which  somewhat  resembles  antimony 
oxide.  It  is  volatile  and  when  touched  with  the  reducing  flame 
gives  a  pale  greenish  color  to  it. 

Tin. 

1.  Reduction  to  Metallic  Globule.  Take  a  small  amount 
of  the  finely  powdered  mineral  and  mix  it  with  five  or  six  volumes 
of  sodium  carbonate  and  considerable  charcoal  dust  and  fuse 
intensely  on  charcoal  in  the  reducing  flame.  Small  bright 
globules  of  metallic  tin  will  result.  They  become  covered  with 
an  oxide  coating  on  cooling.  A  white  and  difficultly  volatile 
tin  oxide  coating  will  form  on  the  charcoal.  If  the  tin  globule 
is  treated  with  a  little  concentrated  nitric  acid,  it  will  be  con- 
verted into  a  white  powder,  which  is  metastannic  acid. 

Titanium. 

1.  Reduction  Test  in  Hydrochloric  Acid.  A  compara- 
tively concentrated  hydrochloric  acid  solution  containing  tita- 
nium will  become  pale  violet  in  color  when  it  is  boiled  with  a 
few  grains  of  metallic  tin.  The  hydrogen  liberated  by  the  ac- 
tion of  the  acid  on  the  tin  is  a  reducing  agent  and  forms  TiCl3 
in  the  solution  which  gives  this  color.  The  color  is  not  a  strong 
one,  and  the  solution  may  have  to  be  evaporated  nearly  to  dry- 
ness  in  order  to  show  it  distinctly.  Most  titanium  minerals 
are  insoluble  in  hydrochloric  acid  and  must  first  be  thoroughly 
fused  with  sodium  carbonate  in  order  to  bring  the  titanium  into 
soluble  form.  The  fusion  is  best  done  by  introducing  the  finely 
powdered  mineral  into  a  sodium  carbonate  bead  made  on  a 
platinum  wire.  Several  such  beads  should  be  used. 

Tungsten. 

1.  Reduction  Test  in  Hydrochloric  Acid.  Treat  a  tungsten 
mineral  with  hydrochloric  acid.  If  it  is  decomposed  by  the  acid' 
a  yellow  precipitate  of  tungstic  oxide,  W03,  will  result.  Add 


112  MANUAL  OF  MINERALOGY 

to  the  acid  a  few  grains  of  metallic  tin  and  boil.  The  hydrogen 
set  free  by  the  action  of  the  hydrochloric  acid  on  the  tin  serves 
as  a  reducing  agent  and  converts  the  yellow  W03  to  a  blue  pre- 
cipitate which  is  a  mixture  of  the  two  oxides  W03  and  W02.  On 
continued  reduction  the  oxide  becomes  all  W02  and  is  brown  in 
color.  The  test  is  similar  to  the  one  for  niobium,  but  is  to  be 
distinguished  from  that,  since  the  blue  color  in  the  tungsten  test 
does  not  disappear  on  dilution  of  the  solution;  and  further,  it 
turns  to  brown  on  continued  reduction.  If  the  tungsten  mineral 
is  not  attacked  by  hydrochloric  acid,  its  powder  must  first  be 
thoroughly  fused  with  sodium  carbonate.  The  resulting  mass 
is  powdered  and  digested  with  water,  which  will  dissolve  the 
sodium  tungstate  formed  during  the  fusion.  After  filtering  the 
reduction  test  is  made  as  described  above. 

Uranium. 

1.  Bead  Tests.  The  tests  for  uranium  consist  in  the  colors  it 
imparts  to  the  fluxes  (see  page  91).  The  yellowish  green  color 
given  to  the  salt  of  phosphorus  bead  when  heated  in  the  oxidiz- 
ing flame  is  the  most  characteristic. 

Vanadium. 

1.  Bead  Tests.  The  tests  for  vanadium  consist  in  the  colors 
it  imparts  to  the  fluxes  (see  page  91).  The  amber  color  given  to 
the  salt  of  phosphorus  bead  when  heated  in  the  oxidizing  flame 
is  the  most  characteristic. 

Zinc. 

1.  Oxide  Coating  on  Charcoal.  Metallic  zinc  is  easily  ob- 
tained from  the  zinc  minerals  by  fusing  them  with  sodium  car- 
bonate on  charcoal  in  the  reducing  flame.  But,  since  the  metal 
is  volatilized  at  a  temperature  considerably  below  that  of  the 
blowpipe  flame,  no  metallic  globule  can  be  formed.  The  metallic 
zinc  is  therefore  all  volatilized,  and,  meeting  the  oxygen  of  the 
surrounding  air,  is  converted  into  the  oxide,  ZnO,  which  drops 
upon  the  charcoal  as  a  nonvolatile  coating,  which  is  yellow  when 


ZINC  113 

hot  but  white  when  cold.  The  coating  deposits  very  close  to 
the  fusion.  It  may  frequently  be  obtained  in  more  distinct  form 
by  making  the  fusion  on  a  loop  of  platinum  wire,  which  is  held 
about  one-quarter  of  an  inch  from  the  surface  of  a  charcoal  block 
and  the  blowpipe  flame  so  directed  that  the  oxide  coating  is  de- 
posited upon  the  charcoal  behind  the  bead.  If  the  coating  is 
moistened  with  a  drop  of  cobalt  nitrate  and  then  heated  intensely 
by  the  blowpipe  flame,  it  will  become  dark  green  in  color. 

2.  Flame  Color.  Some  zinc  minerals,  when  a  fragment  is 
held  in  the  forceps  and  heated  in  the  reducing  flame,  will  show 
a  characteristic  flame  color.  This  is  due  to  the  burning  in  the 
flame  of  the  metallic  zinc  which  has  been  volatilized.  It  takes 
the  form  of  momentary  streaks  or  threads  in  the  flame  and  has 
a  pale  greenish  blue  color. 


IV.     DESCRIPTIVE   MINERALOGY. 
INTRODUCTION. 

DESCRIPTIVE  Mineralogy  should  include  first  of  all  a  descrip- 
tion of  the  crystallographic,  general  physical  .and  chemical  charac- 
ters of  each  mineral  species,  and  should  further  give  an  account 
of  its  mode  of  occurrence  and  characteristic  associations.  The 
localities  at  which  a  mineral  occurs  in  notable  amount  or  quality 
should  also  be  mentioned.  In  the  case  of  minerals  possessing  an 
economic  value,  a  brief  statement  of  their  uses  is  of  interest.  The 
order  in  which  these  various  items  are  given  under  each  mineral 
in  this  Section  is  as  follows: 

1.  Chemical  Composition. 

2.  Crystallization. 

3.  Structure. 

4.  General  Physical  Properties. 

5.  Tests. 

6.  Occurrence. 

7.  Use. 

Descriptive  Mineralogy  should  also  point  out  the  chemical 
and  physical  relationships  existing  between  the  different  mineral 
species.  It  will  be  noted  that  many  minerals  fall  into  definite 
groups  the  members  of  which  have  chemical  and  crystallographic 
features  in  common.  The  most  scientific  classification  of  min- 
erals recognizes  these  facts  and  places  the  minerals  having  analo- 
gous chemical  compositions  together,  and  further  groups  them 
according  to  crystallographic  and  physical  similarities.  Short 
paragraphs  will  be  found  in  various  parts  of  this  Section  which 
explain  more  fully  these  relationships.  The  prominent  chemical 

114 


ELEMENTS  115 

groups  of  this  classification  and  the  order  in  which  they  are 
treated  are  given  below: 

1.  Native  Elements. 

2.  Sulphides,  etc. 

3.  Sulpharsenites,  etc. 

4.  Chlorides,  etc. 

5.  Oxides. 

6.  Carbonates. 

7.  Silicates,  Titanates. 

8.  Niobates,  Tantalates. 

9.  Phosphates,  etc. 

10.  Borates. 

11.  Uranates. 

12.  Sulphates,  etc. 

13.  Tungstates,  Molybdates. 

At  the  end  of  the  matter  descriptive  of  individual  species  will 
be  found  small  sections  devoted  to  (a)  Minerals  of  economic 
importance  arranged  according  to  the  chief  elements  they  con- 
tain; (b)  Occurrence  and  association  of  minerals;  (c)  Table  of 
minerals  arranged  according  to  the  systems  of  crystallization. 

ELEMENTS. 

Comparatively  few  of  the  elements  are  found  in  the  native 
state,  and  moreover,  these  are  in  general  rare  in  occurrence.  The 
elements  occurring  as  minerals  may  be  divided  into  three  classes : 
(1)  Nonmetals,  (2)  Semimetals  and  (3)  Metals.  The  important 
minerals  among  the  nonmetals  are  diamond,  graphite  and  sul- 
phur. The  semimetals  —  tellurium,  arsenic,  antimony  and  bis- 
muth —  belong  together  in  a  crystal  group,  all  of  them  showing 
rhombohedral  crystals  with  closely  agreeing  fundamental  angles. 
The  Gold  Group  is  the  most  important  one  among  the  metals, 
including  the  isometric  minerals,  —  gold,  silver  and  copper.  An- 
other group  contains  the  rare  metals  platinum  and  iron. 


116 


MANUAL  OF  MINERALOGY 


I.   NONMETALS. 
Diamond. 

Composition.     Pure  carbon. 

Crystallization.    Isometric ;  tetrahedral.    Crystals  are  usually 
octahedral  in  habit,  but  the  faces  are  commonly  curved  or  pitted 


Fig.  203.  Fig.  204. 

(Fig.  203).     Curved  faces  of  the  hexoctahedron  are  frequently 
observed    (Fig.   204).     Cubic   and   dodecahedral  planes   rare. 


Fig.  205.  Fig.  206. 

Twins,  with  the  octahedron  as  twinning  plane  (Fig.  205) ;  often 
flattened. 

Structure.  Usually  in  crystals,  but  commonly  distorted  into 
elongated  and  irregular  forms.  At  times  in  spherical  forms  with 
radiating  structure.  Rarely  massive. 

Physical  Properties.  Perfect  cleavage  parallel  to  the  octa- 
hedral faces.  H.  =  10  (hardest  substance  known).  G.  =  3.5. 
Luster  adamantine  or  greasy.  Usually  colorless  or  pale  yellow. 


DIAMOND  117 

Also  pale  shades  of  red,  orange,  green,  blue  and  brown.  Rarely 
in  deep  shades  of  blue,  red  or  green;  at  times  black.  Usually 
transparent  but  may  be  translucent  or  opaque.  Very  high  index 
of  refraction  (diamond  =  2.42,  quartz  =  1.55).  Strong  disper- 
sion of  light.  Electrified  by  friction  and  becomes  phosphorescent 
when  rubbed  with  a  cloth.  Some  stones  after  exposure  to  sun- 
light give  off  a  phosphorescent  glow  in  the  dark. 

Varieties.  Ordinary.  In  rounded  crystals,  some  of  which  are 
perfectly  transparent  and  colorless  (first  water).  Others  are 
faintly  colored  in  various  shades  and  frequently  contain  inclu- 
sions and  are  flawed.  Sort.  In  rounded  spherical  forms  with 
radiating  structure  or  made  up  of  confused  crystalline  aggre- 
gates; usually  gray,  brown  or  black  in  color  and  translucent  to 
opaque.  Fragments  of  crystals  that  are  unavailable  for  cutting 
are  also  frequently  called  bort.  Carbonado  or  black  diamond. 
Massive  with  crystalline  structure  or  granular  to  compact  with- 
out cleavage.  Black  or  grayish  black;  opaque. 

Tests.  To  be  distinguished  by  its  great  hardness,  its  ada- 
mantine luster  and  its  octahedral  cleavage.  Burns  at  a  high 
temperature  to  C02  gas,  leaving  no  ash.  Will  burn  readily  in 
oxygen  gas,  giving  off  a  brilliant  light. 

Occurrence.  The  diamond  is  a  rare  mineral.  It  has  been  found 
in  many  different  localities,  but  only  a  few  have  furnished  the  mineral 
in  notable  amount.  Most  commonly  the  diamond  is  found  in  the 
sands  and  gravels  of  stream  beds,  where  it  has  been  preserved  by  its 
great  hardness  and  fairly  high  specific  gravity.  In  South  Africa 
and  recently  in  Arkansas  it  has  been  found  embedded  in  masses  of 
an  igneous  rock,  known  as  peridotite.  Three  countries  have  up  to 
the  present  furnished  practically  the  entire  world's  output  of  dia- 
monds, namely,  India,  Brazil,  and  South  Africa. 

The  important  diamond  fields  of  India  are  located  in  the  eastern 
and  southern  portions  of  the.  peninsula.  Many  of  the  famous  old 
diamond  fields  in  this  region  are  now  abandoned,  but  work  is  still 
carried  on  by  the  natives  in  the  mines  in  a  district  lying  to  the  south 
of  Allahabad  and  Benares.  Many  of  the  world's  famous  diamonds 
were  found  in  India,  but  at  present  the  yield  is  small. 

Diamonds  were  discovered  in  Brazil  in  the  first  half  of  the  eight- 
eenth century,  and  have  been  mined  there  ever  since.  At  present, 
however,  the  production  is  comparatively  small.  They  are  found  in 
the  stream  gravels  in  several  different  districts,  the  two  most  im- 


118  MANUAL  OF  MINERALOGY 

portant  being  located  in  the  provinces  of  Minas  Geraes  and  Bahia. 
The  city  of  Diamantina,  Minas  Geraes,  is  situated  in  the  center  of  the 
most  productive  field,  the  diamonds  being  found  chiefly  in  the  gravels 
of  the  Rio  Jequitinhonha  and  Rio  Doce.  Extensive  upland  deposits 
of  diamond-bearing  gravels  and  clays  are  also  worked. 

About  96  per  cent  of  the  world's  output  of  diamonds  comes  at 
present  from  South  Africa.  The  first  diamonds  were  discovered  in 
the  gravels  of  the  Vaal  River  in  1867.  The  diamond-bearing  gravels 
covered  a  considerable  area  but  were  not  very  thick.  Later  the 
diamonds  were  discovered  embedded  in  the  rock  of  several  volcanic 
necks  located  near  the  present  town  of  Kimberly  in  Griqualand- 
West,  south  of  the  Vaal  River,  near  the  boundary  of  the  Orange 
Free  State.  The  diamonds  in  this  district  were  first  discovered  in  the 
soil  resulting  from  the  disintegration  of  the  underlying  diamond- 
bearing  rock.  This  soil  was  colored  yellow  by  iron  oxides,  and  was 
known  as  the  "yellow  ground."  The  underlying,  undecomposed 
peridotite  rock  from  which  the  diamonds  are  obtained  at  present 
is  called  the  "blue  ground."  The  principal  mines  are  the  Kimberly, 
Du  Toitspan,  De  Beers  and  Bultfontein,  near  Kimberly,  the  Jagers- 
fontein  in  the  Orange  Free  State,  and  the  Premier  in  the  Transvaal. 
The  mines  were  originally  worked  as  open  pits,  but,  as  they  have 
increased  in  depth,  underground  methods  have  been  adopted.  The 
blue  rock  containing  the  diamonds  is  brought  to  the  surface,  crushed 
into  coarse  fragments  and  spread  out  on  platforms  to  gradually  dis- 
integrate under  atmospheric  influences.  The  resulting  gravel  is 
washed  over  and  concentrated,  the  diamonds  being  finally  separated 
on  shaking  tables  that  have  been  coated  with  grease,  to  which  the 
diamond  crystals  stick,  while  the  rest  of  the  material  is  washed 
away.  Diamonds  have  also  recently  been  discovered  in  alluvial 
deposits  near  Liideritzbuchte,  German  Southwest  Africa. 

Diamonds  have  been  found  sparingly  in  various  parts  of  the 
United  States.  Small  stones  have  occasionally  been  discovered  in 
the  stream  sands  along  the  eastern  slope  of  the  Appalachian  Moun- 
tains from  Virginia  south  to  Georgia.  Diamonds  have  also  been 
reported  from  the  gold  sands  of  northern  California  and  southern 
Oregon.  Sporadic  occurrences  of  diamonds  have  been  noted  in  the 
glacial  drift  in  Wisconsin,  Michigan  and  Ohio.  In  1906  the  first 
diamond  was  found  at  a  new  locality  situated  near  Murfreesboro, 
Pike  County,  Arkansas.  The  stones  are  found  here  not  only  in  the 
detrital  soil  but  also  embedded  in  the  underlying  peridotite  rock  in 
a  manner  quite  similar  to  that  of  the  South  African  occurrence. 

General.  The  diamond  is  the  most  important  of  the  gem  stones. 
Its  value  depends  upon  its  hardness,  its  brilliancy,  which  is  due  to 
its  high  index  of  refraction,  and  to  its  "fire,"  which  is  due  to  its  strong 
dispersion  of  light  into  the  prismatic  colors.  In  general  the  most 


DIAMOND  119 

valuable  stones  are  those  which  are  flawless  and  colorless  or  possess 
a  "blue-white"  color.  A  faint  straw-yellow  color,  which  diamond 
often  shows,  detracts  much  from  its  value.  Deep  shades  of  yellow, 
red,  green  or  blue  are  greatly  prized,  and  fine  stones  of  these  colors 
bring  very  high  values. 

The  diamond  is  cut  by  first  cleaving  off  any  undesirable  or  flawed 
portions  of  the  crystal  and  then  grinding  facets  upon  it  by  use  of 
diamond  powder.  The  crystal  is  fixed  at  the  end  of  a  stick  by  means 
of  soft  solder,  leaving  the  part  projecting  which  is  to  be  cut.  A  cir- 
cular plate  of  soft  iron  is  then  charged  with  diamond  dust,  and  this 
by  its  revolution  grinds  and  polishes  the  stone.  Most  diamonds  are 
cut  into  the  form  known  as  the  brilliant  (see  Fig.  206).  This  is  a 
stone  cut  with  a  large  eight-sided  facet  on  top  and  a  series  of  small 
inclined  faces  around  it.  The  lower  half  consists  of  steeply  inclined 
faces  giving  the  stone  on  this  side  a  pyramidal  shape.  The  depth 
of  a  brilliant  is  nearly  equal  to  its  breadth,  and  it,  therefore,  can  only 
be  cut  from  a  thick  stone.  Thinner  stones,  in  proportion  to  the 
breadth,  are  cut  into  what  is  known  as  the  rose  diamond.  This  is 
a  stone  which  has  its  upper  surface  covered  with  small  triangular 
facets.  Its  lower  surface  may  be  one  plane  face,  or  the  cutting  of 
the  upper  half  may  be  duplicated.  With  exceptional-shaped  stones 
other  cuttings  are  used. 

The  value  of  a  cut  diamond  depends  upon  its  color  and  purity, 
upon  the  skill  with  which  it  has  been  cut  and  upon  its  size.  A  one- 
carat  stone  weighs  205  milligrams,  and  if  cut  in  the  form  of  a  brilliant 
would  be  6.25  millimeters  in  diameter  and  4  millimeters  in. depth, 
and  if  of  good  color  would  be  valued  from  $150  to  $175.  A  two- 
carat  stone  of  the  same  quality  would  have  a  value  three  or  four 
times  as  great. 

Famous  Stones.  The  older  famous  diamonds  include  the  follow- 
ing: the  Kohinoor,  weighing  106  carats,  is  one  of  the  crown  jewels  of 
Great  Britain;  the  Regent  or  Pitt,  weighing  136  carats,  belonging  to 
France;  the  Orloff,  which  is  mounted  in  the  Russian  imperial  scepter, 
weighs  193  carats;  Austria  owns  the  Florentine  yellow  diamond, 
which  weighs  139  carats;  the  Star  of  the  South,  weighing  125  carats, 
is  said  to  be  in  India. 

Large  stones  found  more  recently  in  South  Africa  include  the 
following:  The  Victoria  or  Imperial,  which  weighed  457  carats  when 
found,  and  230  when  cut.  It  was,  however,  later  recut,  its  present 
weight  being  180  carats.  The  Stewart  weighed  before  and  after 
cutting  288  and  120  carats  respectively.  The  Tiffany  diamond, 
which  is  of  a  brilliant  yellow  color,  weighs  125  carats.  The  Colenso 
diamond,  presented  to  the  British  Museum  in  1887  by  John  Ruskin, 
weighs  129|  carats.  The  Excelsior  diamond,  found  at  Jagersfontein 
in  1903,  is  now  known  as  the  Jubilee,  and  weighs  239  carats.  The 


120  MANUAL  OF  MINERALOGY 

Cullinan  or  Premier  diamond  was  found  at  the  Premier  Mine,  Trans- 
vaal, and  was  the  largest  stone  ever  found,  weighing  3024  carats  or 
1.7  pounds  troy,  and  measured  4  by  2\  by  2  inches.  This  stone  was 
presented  to  King  Edward  VII  by  the  Transvaal  Government  and 
has  been  cut  into  9  large  stones,  the  larger  ones  weighing  516,  309, 
92  and  62  carats  respectively,  and  into  96  smaller  brilliants. 

Name.  The  name  diamond  comes  from  the  Greek  word 
adamas,  meaning  "  in  vincible." 

Use.  In  addition  to  its  wide  use  as  a  gem,  the  diamond  is 
extensively  used  as  an  abrasive.  Crystal  fragments  are  used  to 
cut  glass.  The  fine  powder  is  employed  in  grinding  and  polish- 
ing diamonds  and  other  stones.  The  noncrystalline,  opaque 
varieties,  especially  that  known  as  carbonado,  are  used  in  the 
bits  of  diamond  drills.  These  drills  are  frequently  employed 
in  mining  operations  to  explore  the  rocks  and  to  determine  the 
position  and  size  of  ore  bodies.  Recently  the  diamond  has  been 
used  in  wiredrawing  and  in  the  making  of  tungsten  filaments 
for  electric  lights. 

Graphite. 

Composition.  Carbon,  like  the  diamond.  Sometimes  im- 
pure with  iron  oxide,  clay,  etc. 

Crystallization.  Hexagonal-rhombohedral.  In  tabular  crys- 
tals with  hexagonal  outline.  Prominent  basal  plane.  Distinct 
planes  of  other  forms  very  rare.  Rhombohedral  symmetry 
sometimes  shown  by  triangular  markings  on  base. 

Structure.  In  foliated  masses;  scaly;  granular  to  compact; 
earthy.  Sometimes  in  globular  forms  with  radiated  structure. 

Physical  Properties.  Perfect  basal  cleavage.  H.  =  1-2  (read- 
ily marks  paper  and  soils  the  fingers).  G.  =  2.2.  Luster  metal- 
lic, sometimes  dull  earthy.  Black  color  with  brownish  tinge. 
Black  streak.  Greasy  feel.  Folia  flexible  but  not  elastic. 

Tests.  Infusible.  Very  refractory  in  its  chemical  nature. 
Recognized  by  its  color,  foliated  structure  and  softness.  Dis- 
tinguished from  molybdenite  by  the  brownish  tinge  to  K  black 
color  (molybdenite  has  a  blue  tone)  and  the  lack  of  cnemical 
tests. 


GRAPHITE  121 

Occurrence.  Graphite  most  commonly  occurs  in  metamorphic 
rocks,  such  as  crystalline  limestones,  schists  and  gneisses.  It  may 
occur  as  large  crystalline  plates  inclosed  in  the  rock  or  disseminated 
in  small  flakes  in  sufficient  amount  to  form  a  considerable  proportion 
of  the  rock.  In  these  cases,  it  has  probably  been  derived  from  carbon 
material  of  organic  origin  which  has  been  converted  into  graphite 
during  the  metamorphism  of  the  rock.  Instances  are  known  in 
which  coal  beds,  under  influence  of  strong  metamorphic  action,  such 
as  the  intrusion  into  them  of  an  igneous  rock,  have  in  a  greater  or 
less  degree  been  converted  into  graphite.  Examples  of  such  an 
occurrence  are  to  be  found  in  the  graphitic  coals  of  Rhode  Island, 
and  in  the  coal  fields  of  Sonora,  Mexico.  Graphite  also  occurs  in 
fissure  veins  associated  with  calcite,  quartz,  orthoclase,  pyroxene, 
etc.  An  example  of  such  veins  is  to  be  found  in  the  deposits  at 
Ticonderoga,  New  York.  Here  the  veins  traverse  a  gneiss  and 
besides  the  graphite  contain  quartz,  biotite,  orthoclase,  tourmaline, 
apatite,  pyrite,  titanite,  etc.  The  graphite  may  have  been  formed 
in  these  veins  from  hydrocarbons  introduced  into  them  during  the 
metamorphism  of  the  region  and  derived  from  the  surrounding 
carbon-bearing  rocks.  Graphite  occurs  occasionally  as  an  original 
constituent  in  igneous  rocks.  It  has  been  observed  in  the  basalts 
of  Ovifak,  Greenland,  in  an  elasolite  syenite  from  India,  in  a  granite 
pegmatite  from  Maine,  in  meteorites,  etc. 

The  most  productive  deposits  of  graphite  at  present  are  on  the 
island  of  Ceylon,  where  it  occurs  in  coarsely  foliated  masses  in  veins 
in  gneiss.  It  occurs  in  large  amounts  in  various  localities  in  Austria, 
Italy,  India,  Mexico,  etc.  The  chief  deposits  in  the  United  States 
are  in  the  Adirondack  region  of  New  York,  in  Essex,  Warren,  Wash- 
ington and  Saratoga  counties. 

Artificial.  Artificial  graphite  is  manufactured  on  a  large  scale  in 
the  electrical  furnaces  at  Niagara  Falls.  Anthracite  coal  with  a 
small  amount  of  evenly  distributed  ash  is  subjected  to  the  intense 
heat  of  the  electrical  current  and  converted  into  graphite.  The 
output  of  artificial  graphite  is  considerably  in  excess  of  that  of  the 
natural  mineral. 

Name.  Derived  from  the  Greek  word  "to  write." 
Use.  Used  in  the  manufacture  of  refractory  crucibles  for 
the  steel,  brass  and  bronze  industries.  Most  of  the  graphite 
used  in  this  way  is  imported  from  Ceylon.  Used  widely,  when 
mixed  with  oil,  as  a  lubricant.  Mixed  with  fine  clay,  it  forms 
the  "lead"  of  pencils.  Much  of  the  graphite  used  in  the  United 
States  for  this  purpose  comes  from  Sonora,  Mexico.  Used  in 
the  manufacture  of  a  protective  paint  for  structural  iron  and 


122 


MANUAL  OF  MINERALOGY 


steel  works.     Used  in  the  coating  of  foundry  facings,  for  elec- 
trodes, stove  polishes,  in  electrotyping,  etc. 

Sulphur. 

Composition.    Sulphur;  often  impure  with  clay,  bitumen,  etc. 

Crystallization.  Orthorhombic.  Pyramidal  in  habit  (Fig. 
207).  Often  with  two  pyramids,  brachydome  and  base  in  com- 
bination (Figs.  208  and  209). 


Fig.  207. 


Fig.  209. 


Structure.  Often  in  irregular  masses  imperfectly  crystallized. 
Massive,  reniform,  stalactitic,  as  incrustations,  earthy. 

Physical  Properties.  H.  =  1.5-2.5.  G.  =  2.05-2.09.  Res- 
inous luster.  Color  sulphur-yellow,  varying  with  impurities  to 
yellow  shades  of  green,  gray  and  red.  Transparent  to  opaque. 
Imperfect  conductor  of  heat.  When  a  fragment  is  held  in  the 
hand  close  to  the  ear  it  will  be  heard  to  crack.  This  is  due  to 
the  expansion  of  the  surface  layers  because  of  the  heat  from  the 
hand,  while  the  interior,  on  account  of  the  slow  heat  conductivity, 
is  unaffected.  Crystals  of  sulphur  should,  therefore,  be  handled 
with  care. 

Tests.  Fusible  at  1  and  burns  with  a  blue  flame  giving  strong 
odor  of  sulphur  dioxide.  Sublimes  in  C.  T.  giving  a  red  to  dark 
yellow  liquid  when  hot,  yellow  solid  when  cold.  Told  by  its 
yellow  color  and  the  ease  with  which  it  burns. 

Occurrence.  Found  either  associated  with  beds  of  gypsum,  as 
an  alteration  product  of  a  sulphate,  or  in  connection  with  active  or 
extinct  volcanoes,  as  a  result  of  fumerole  action.  Sometimes  in 
connection  with  sulphides  in  metallic  veins  and  derived  from  their 


ARSENIC  123 

oxidation.  Found  in  large  deposits  and  in  fine  crystals  near  Gir- 
genti,  Sicily,  associated  with  celestite,  gypsum,  calcite,  aragonite, 
etc.;  also  in  connection  with  the  volcanoes  of  Mexico,  Hawaii, 
Japan,  Iceland,  etc.  In  the  United  States  is  mined  in  Calsasieu 
Parish,  Louisiana,  and  in  Wyoming  and  Utah. 

Use.  Used  in  the  manufacture  of  sulphuric  acid,  in  the  manu- 
facture of  matches,  gunpowder,  fireworks,  insecticides,  for  vul- 
canizing rubber  and  in  medicine. 


II.  SEMIMETALS. 
Tellurium. 

Native  tellurium  with  sometimes  a  small  amount  of  selenium, 
gold,  iron,  etc.  Hexagonal-rhombohedral.  Crystals  rare;  usually 
minute  hexagonal  prisms  with  rhombohedral  terminations.  Com- 
monly massive,  columnar  to  fine  granular.  Perfect  prismatic  cleav- 
age. H.  =  2-2.5.  G.  =  6.1-6.3.  Metallic  luster.  Tin-white  color. 
Gray  streak.  Wholly  volatile  B.  B.  Fusible  at  1.  On  charcoal 
tinges  reducing  flame  green  and  gives  a  white  oxide  coating.  Heated 
with  concentrated  sulphuric  acid  gives  deep  red  color  to  solution. 
A  rare  species,  found  usually  associated  with  the  rare  teilurides 
of  gold  and  silver.  Occurs  with  sylvanite  near  Zalathna,  Transyl- 
vania, at  the  Good  Hope  Mine,  Vulcan,  Colorado,  and  in  other  dis- 
tricts in  that  state.  Tellurium  has  little  commercial  value. 

Arsenic. 

Composition.  Arsenic,  often  with  some  antimony  and  traces 
of  iron,  silver,  gold,  bismuth,  etc. 

Crystallization.     Hexagonal-rhombohedral.     Crystals  rare. 

Structure.  Usually  granular  massive,  sometimes  reniform 
and  stalactitic. 

Physical  Properties.  Perfect  basal  cleavage.  H.=3.5.  G.=5.7. 
Metallic  luster.  Color  tin-white  on  fresh  fracture,  tarnishes 
on  exposure  to  dark  gray.  Gray  streak. 

Tests.  Volatile  without  fusion.  B.  B.  on  charcoal  gives 
white  volatile  coating  of  arsenious  oxide  and  odor  of  garlic.  In 
0.  T.  gives  volatile  crystalline  deposit  of  arsenious  oxide.  In 
C.  T.  gives  arsenic  mirror. 


124  MANUAL  OF  MINERALOGY 

Occurrence.  A  comparatively  rare  species  found  in  veins  in  crys- 
talline rocks  associated  with  antimony  minerals,  the  ruby  silvers, 
realgar,  orpiment,  sphalerite,  etc.  Found  in  the  silver  mines  of 
Saxony,  in  Bohemia,  Norway,  Zmeov  in  Siberia,  Chile,  Mexico. 
Sparingly  in  the  United  States. 

Name.  The  name  arsenic  is  derived  from  a  Greek  word 
meaning  masculine,  a  term  first  applied  to  the  sulphide  of  arsenic 
on  account  of  its  potent  properties. 

Use.     Very  minor  ore  of  arsenic. 

Antimony. 

Composition.  Antimony,  with  (at  times)  small  amounts  of 
arsenic,  iron  or  silver. 

Crystallization.  Hexagonal-rhombohedral.  Distinct  crystals 
rare. 

Structure.  Usually  in  granular  masses  showing  distinct  cleav- 
age; radiated;  botryoidal. 

Physical  Properties.  Perfect  basal  cleavage.  H.  =  3-3.5. 
G.  =  6.6-6.7.  Metallic  luster.  Tin-white  color.  Gray  streak. 

Tests.  Easily  and  completely  volatile.  Fusibility  1.  When 
heated  on  charcoal  gives  a  dense  white  coating  of  antimony 
trioxide.  Heated  in  0.  T.  gives  a  white,  slowly  volatile  subli- 
mate of  antimony  trioxide. 

Occurrence.  A  rare  species,  found  usually  in  connection  with 
silver  veins  and  associated  with  arsenic  and  antimony  compounds. 
Occurs  at  Sala,  Sweden;  Andreasberg,  Harz  Mountains;  at  Pfibram, 
Bohemia;  Allemont,  France;  Chile;  South  Ham,  Canada;  York 
County,  New  Brunswick,  etc. 

Use.     Minor  ore  of  antimony. 

Bismuth. 

Composition.  Bismuth,  with  sometimes  small  amounts  of 
arsenic,  sulphur,  tellurium. 

Crystallization.  Hexagonal-rhombohedral.  Distinct  crys- 
tals rare. 

Structure.  Usually  laminated  and  granular;  sometimes  re- 
ticulated or  arborescent. 


GOLD  125 

Physical  Properties.  Basal  and  rhombohedral  cleavage.  H.  = 
2-2.5.  G.  =  9.8.  Sectile.  Brittle.  Metallic  luster.  Color 
silver-white  with  decided  reddish  tone.  Streak  silver-white, 
shining. 

Tests.  Fusible  at  1.  B.  B.  on  charcoal  gives  metallic  globule 
and  yellow  to  white  coating  of  bismuth  oxide.  The  globule  is 
somewhat  malleable  but  cannot  be  hammered  into  as  thin  a 
sheet  as  in  the  case  of  lead.  Mixed  with  potassium  iodide  and 
sulphur  and  heated  on  charcoal  gives  a  brilliant  yellow  tp  red 
Boating.  Recognized  chiefly  by  its  laminated  structure,  its 
reddish  silver  color  and  its  sectility. 

Occurrence.  A  comparatively  rare  mineral,  occurring  usually  in 
connection  with  ores  of  silver,  cobalt,  lead  and  zinc.  Found  in  the 
silver  veins  of  Saxony;  in  Norway  and  Sweden;  Cornwall,  England; 
with  the  silver  and  cobalt  minerals  at  Cobalt,  Ontario,  Canada;  only 
sparingly  in  the  United  States. 

Use.  Ore  of  bismuth.  The  greater  part  of  the  bismuth  of 
commerce  is  produced  from  the  sulphide,  bismuthinite,  or  from 
other  ores  that  contain  a  small  per  cent  of  the  metal.  It  is 
chiefly  employed  in  the  manufacture  of  low-fusing  alloys  which 
are  used  as  safety  plugs  in  boilers  and  in  automatic  fire  sprinklers, 
etc.  Its  salts  are  used  in  medicine. 

III.   METALS. 

GOLD   GROUP.     ISOMETRIC. 
Gold. 

Composition.  Gold,  commonly  alloyed  with  small  amounts 
of  silver  and  at  times  with  traces  of  copper  and  iron.  Ordinarily, 
native  gold  contains  varying  amounts  of  alloyed  silver  up  to 
16  per  cent.  California  gold  contains  between  10  and  15  per 
cent  of  silver.  The  greater  part  of  native  gold  is  about  90  per 
cent  "fine"  or  contains  10  per  cent  of  other  metals.  Gold  con- 
taining unusually  high  percentages  of  silver  (25  to  40  per  cent) 
is  known  as  electrum. 

Crystallization.  Isometric.  Crystals  are  commonly  octahe- 
dral in  habit,  showing  also  at  times  the  faces  of  the  dodeca- 


126 


MANUAL  OF  MINERALOGY 


hedron,  cube,  etc.  (see  Figs.  210,  211  and  212) .     Often  in  arbores- 
cent crystal  groups  with  crystals  elongated  in  the  direction  of  an 


Fig.  210. 
Octahedron. 


Fig.  211. 
Dodecahedron. 


Fig.  212. 
Cube  and  Octahedron. 


octahedral  axis.  Crystals  irregularly  distorted  and  passing  into 
filiform,  reticulated  and  dendritic  shapes. 

Structure.  Usually  in  irregular  plates,  scales  or  masses. 
Seldom  definitely  crystallized. 

Physical  Properties.  H.  =  2.5-3.  G.  =  15.6-19.3  (becomes 
greater  as  the  percentages  of  the  other  metals  present  decrease). 
Very  malleable  and  ductile.  Color  various  shades  of  yellow, 
depending  upon  purity,  becoming  paler  with  increase  in  the  per- 
centage of  silver  present. 

Tests.  Easily  fusible  at  2.5-3.  Insoluble  in  ordinary  acids 
but  soluble  in  a  mixture  of  hydrochloric  and  nitric  acids.  To 
be  distinguished  from  certain  yellow  sulphides  (particularly  pyrite 
and  chalcopyrite)  and  from  yellow  flakes  of  altered  micas  by  its 
malleability,  its  insolubility  and  its  great  weight. 

Occurrence.  Although  gold  is  a  rare  element,  it  is  to  be  found 
widely  distributed  in  nature,  occurring  in  small  amounts.  Its  pres- 
ence as  a  primary  constituent  of  igneous  rocks,  more  particularly  of 
the  acidic  type,  has  been  abundantly  proved.  It  is  to  be  found  most 
commonly  in  quartz  veins.  It  occurs  in  detrital  sands  and  gravels 
in  what  are  known  as  placer  deposits.  It  is  present  in  small  amounts 
in  sea  water.  It  is  important  to  note  that  gold  occurs  almost  wholly 
as  the  native  metal,  the  only  class  of  compounds  which  it  forms  in 
nature  being  the  tellurides. 

The  chief  source  of  gold  is  the  gold-quartz  veins.  It  occurs  in 
these  veins  usually  as  very  small  specks  scattered  uniformly  through- 
out the  quartz  gangue.  The  contents  of  these  veins  are  in  general 


GOLD  127 

considered  to  have  been  deposited  from  ascending  mineral-bearing 
solutions.  That  gold  is  capable  of  solution  and  subsequent  precipi- 
tation by  means  of  underground  waters  has  been  repeatedly  demon- 
strated. In  the  majority  of  veins  the  gold  is  so  finely  divided  and 
uniformly  distributed  that  its  presence  in  the  ore  cannot  be  detected 
with  the  eye.  It  is  interesting  to  note  that  with  the  value  of  gold 
at  $20.67  a  troy  ounce,  ore  which  contains  one  per  cent  of  gold  by 
weight  would  be  worth  $6028  to  the  ton,  while  an  ore  containing 
only  0.01  per  cent  of  gold  would  still  be  a  rich  ore,  having  a  value  of 
$60  per  ton.  Ores  are  mined  at  a  profit  sometimes  which  contain 
only  0.001  per  cent  of  gold  and  yield  but  $6  to  the  ton.  So  it  might 
be  quite  impossible  x>  detect  the  presence  of  gold  in  a  valuable  ore 
by  any  ordinary  tests.  A  definite  estimation  of  the  amount  of  gold 
present  by  means  of  a  careful  assay  is  the  only  way  usually  to  deter- 
mine the  value  of  an  ore.  But  occasionally,  under  favorable  con- 
ditions, the  gold  may  collect  in  larger  amounts,  in  nests  and  pockets 
in  the  veins,  occurring  usually  as  irregular  plates  and  masses  between 
the  crystals  of  quartz.  In  the  quartz  veins  the  gold  is  frequently 
associated  with  sulphides,  particularly  with  pyrite.  It  is  thought 
that  the  gold  does  not  exist  in  any  chemical  combination  with  the 
pyrite,  but  has  ,the  same  mechanical  relation  to  it  that  it  has  to  the 
quartz.  The  upper  portions  of  the  gold-quartz  veins  as  a  rule  have 
been  enriched  in  their  values.  The  gold  present  in  this  upper  zone 
was  in  part  deposited  contemporaneously  with  the  formation  of  the 
vein,  but  frequently  the  greater  part  has  been  transported,  either 
in  solution  or  by  mechanical  settling,  from  that  upper  portion  of  the 
vein  which  has  been  gradually  eroded  away!  And  so  the  gold  in 
this  part  of  the  vein  represents  the  concentration  in  a  small  space 
of  the  original  gold  content  of  a  much  greater  length  of  vein.  By 
the  oxidation  of  the  gold-bearing  sulphides  originally  deposited  in 
this  portion  of  the  vein  the  gold  embedded  in  them  has  been  set  free, 
rendering  the  gold  easy  of  extraction.  Ores  that  contain  the  gold 
free  from  intimate  association  with  sulphides  are  known  as  "free- 
milling"  because  their  gold  content  can  be  recovered  by  amalgama- 
tion with  the  mercury  of  the  plates  over  which  the  finely  crushed  ore 
runs  from  the  stamp  mill.  Where  sulphides  are  present  in  any 
quantity  all  of  the  gold  cannot  be  recovered  by  amalgamation  and  a 
chemical  process,  either  the  cyanide  or  chlorination  process,  must 
be  used,  either  alone,  or  in  addition  to  the  amalgamation. 

In  addition  to  occurring  with  quartz  and  pyrite,  gold  has  been 
found  associated  with  chalcopyrite,  sphalerite,  galena,  stibnite, 
cinnabar,  arsenopyrite,  limonite,  calcite,  etc. 

Gold,  on  account  of  its  great  weight,  is  mechanically  sorted  in 
running  water  from  the  lighter  material  of  the  sands  and  gravels  in 
which  it  may  occur.  In  this  way  a  concentration  frequently  takes 


128  MANUAL  OF  MINERALOGY 

place  in  stream  beds  and  gold  placer  deposits  are  formed.  In  general 
these  deposits  will  be  found  where  the  current  of  the  water  has  been 
suddenly  checked  and  the  heaviest  particles  of  its  load  dropped  in 
the  bottom  of  the  stream.  Sand  bars,  etc.,  formed  in  this  way  may 
contain  rich  placer  deposits.  Irregularities  in  the  bottom  of  a 
stream  frequently  act  as  natural  riffles  and  catch  behind  them  the 
heavier  gold  traveling  along  the  bottom  of  the  stream.  In  general, 
also,  such  deposits  will  be  richer  as  the  stream  is  ascended  and  the 
original  veins  from  which  the  gold  has  been  derived  are  approached. 
The  larger  masses  of  gold  which  have  been  rolled  together  by  the 
action  of  the  stream  are  called  nuggets.  These  sometimes  attain 
considerable  size.  The  very  fine  gold  which  is  known  as  float  gold 
may  be  carried  by  the  streams  for  long  distances. 

In  California,  at  the  close  of  the  glacial  epoch,  large  amounts  of 
gold-bearing  gravels  were  deposited  in  the  stream  beds.  Subse- 
quent changes  in  the  elevation  of  the  country  and  extensive  lava 
flows  have  caused  a  rearrangement  of  the  drainage,  and  in  places 
these  old  gravel  beds  are  to  be  found  to-day  upon  the  liillsides  and 
are  known  as  the  hill  gravels.  In  places  they  have  been  covered 
over  with  lava  flows  and  so  preserved  from  erosion.  At  Cape  Nome, 
Alaska,  the  beach  sands  contained  gold,  where  by  the  action  of  the 
waves  the  gold  has  been  concentrated  to  form  placer  deposits. 

The  important  gold-producing  states  and  territories  of  the 
United  States,  in  their  approximate  order  of  importance,  are  Colo- 
rado, Alaska,  California,  Nevada,  South  Dakota,  Utah,  Montana,  • 
Arizona  and  Idaho.  There  are  several  other  states  that  also  produce 
the  metal,  but  in  comparatively  small  amounts.  The  most  im- 
portant gold-producing  districts  of  California  are  those  of  the  series 
of  gold-quartz  veins  known  as  the  Mother  Lode  which  lie  along  the 
western  slope  of  the  Sierras  in  Nevada,  Amador,  Calaveras,  Eldorado, 
Tuolumne  and  Mariposa  counties.  Between  one-third  and  one-half 
of  California's  gold  production  comes  from  placer  deposits,  mostly 
worked  by  dredging  operations  in  Butte  and  Yuba  counties.  The 
gold  of  Alaska  has  been  derived  chiefly  from  placer  deposits,  but 
recently  the  vein  deposits  have  been  of  .increasing  importance.  The 
chief  producing  districts  are  the  Yukon  Basin,  the  Fairbanks  Dis- 
trict and  the  Seward  Peninsula,  including  Nome.  Although  Colo- 
rado is  one  of  the  first  states  in  the  production  of  gold,  about  one- 
half  of  its  output  comes  from  the  Cripple  Creek  District  in  Teller 
County,  where  the  gold  occurs  only  sparingly  native,  but  chiefly  in 
the  form  of  the  tellurides,  sylvanite  and  calaverite.  The  other 
chief  producing  counties  are  San  Miguel  and  Ouray  in  the  San  Juan 
District,  and  Lake  County,  containing  the  Leadville  District,  and 
Gilpin,  Clear  Creek  and  Boulder  counties  in  the  Clear  Creek  District. 
The  chief  gold  districts  of  Nevada  are  Goldfield  and  Tonopah  and 


SILVER  129 

other  smaller  camps  in  Nye  and  Esmeralda  counties.  The  gold 
from  South  Dakota  comes  from  the  Black  Hills,  the  Homestake  Mine 
at  Lead  being  the  largest  producer.  The  gold-producing  districts 
of  Utah  are  the  Tintic  and  Bingham  districts  in  Juab  and  Salt  Lake 
counties  respectively,  and  the  Mercur  District  in  Tooele  County. 

Important  foreign  gold-producing  countries  are  as  follows:  South 
Africa,  Australia,  Russia,  Mexico  and  Canada.  The  region  known 
as  the  Rand,  near  Johannesburg  in  the  Transvaal,  South  Africa,  is 
the  most  productive  gold  district  in  the  world.  The  gold  occurs 
here  scattered  throughout  inclined  beds  or  " reefs"  of  a  quartzose 
conglomerate,  which  has  been  mined  in  enormous  amounts  and  to 
great  depths.  Australia  has  the  following  chief  gold  districts: 
Kalgoorlie  in  western  Australia  (largely  tellurides),  Ballarat  and 
Bendigo  in  Victoria,  Mount  Morgan  in  Queensland  and  various  fields 
in  New  South  Wales.  In  Russia  gold  is  mined  in  western  Siberia 
and  the  Urals,  in  the  Irkutsk  Province,  in  Transbaikalia  and  Amur. 
The  production  of  Mexico  comes  chiefly  from  the  districts  of  Guana- 
juato, El  Oro  and  Dolores. 


Silver. 

Composition.  Silver,  frequently  containing  small  amounts  of 
alloyed  copper  and  gold,  more  rarely  traces  of  platinum,  anti- 
mony, bismuth,  mercury. 

Crystallization.  Isometric.  Crystals  commonly  distorted  and 
in  branching,  arborescent  or  reticulated  groups. 

Structure.  Commonly  in  irregular  masses,  plates,  scales,  etc.; 
at  times  as  coarse  or  fine  wire. 

Physical  Properties.  H.  =  2.5-3.  G.  =  10.1-11.1,  pure  10.5. 
Malleable  and  ductile.  Color  silver-white,  often  tarnished  to 
brown  or  gray-black. 

Tests.  Easily  fusible  at  2  to  bright  globule.  No  oxide  coat- 
ing on  charcoal.  Easily  soluble  in  nitric  acid,  giving  on  addition 
of  hydrochloric  acid  a  curdy  white  precipitate  of  silver  chloride, 
which  turns  dark  on  exposure  to  light.  Deposited  from  its  solu- 
tion by  action  of  a  clean  copper  plate. 

Occurrence.  Occurs  usually  as  small  irregular  flakes  and  masses 
disseminated  through  various  vein  minerals,  often  invisible.  Found 
associated  with  native  copper,  galena,  argentite,  chalcocite,  the  ruby 
silvers,  tetrahedrite,  calcite,  barite,  etc.  While  native  silver  is  not 


130 


MANUAL  OF  MINERALOGY 


an  uncommon  mineral,  the  larger  part  of  the  world's  output  of  the 
metal  is  obtained  from  its  various  compounds  with  sulphur,  anti- 
mony, arsenic,  etc.  Most  of  the  native  silver  occurring  in  nature  is 
probably  secondary  in  its  origin,  having  been  derived  by  reduction 
from  some  of  its  compounds. 

Native  silver  has  been  found  in  the  United  States  with  native 
copper  in  the  copper  mines  of  Lake  Superior;  in  crystal  groups  at 
the  Elkhorn  Mine,  Montana;  in  large  masses  in  the  silver  mines  at 
Aspen,  Colorado.  Is  found,  at  present,  in  large  quantities  as  platy 
masses,  associated  with  various  cobalt  and  nickel  minerals,  at  Cobalt, 
Ontario,  Canada.  An  important  silver  ore  in  the  mines  of  Chihua- 
hua, Guanajuato,  Durango,  Sinaloa  and  Sonora,  Mexico.  Occurs 
commonly  in  the  mines  of  Peru.  Was  found  in  large  masses,  one 
of  which  weighed  500  pounds,  in  the  mines  at  Kongsberg,  Norway. 
One  of  the  ores  of  the  silver  mines  of  Saxony  and  Bohemia. 

Use.  Silver  is  used  for  ornamental  purposes,  for  coinage, 
plating,  etc.  It  is  usually  alloyed  with  copper.  The  standard 
silver  coin  in  the  United  States  contains  one  part  of  copper  to 
nine  parts  of  silver. 

Copper. 

Composition.  Copper,  often  containing  small  amounts  of 
silver,  bismuth,  mercury,  etc. 

Crystallization.     Isometric.    Tetrahexahedron  faces  common 
on  crystals,  (see  Fig.  213).    Also  cube  and  dodecahedron.   Crys- 
tals usually  distorted  and  in  branching 
and   arborescent  groups,    (see    PL    IV). 
Structure.   Usually  in  irregular  masses, 
plates,  scales,  etc.     In  twisted  and  wire- 
like  forms. 

Physical  Properties.    H.  =  2.5-3. 
G.  =  8.8-8.9.     Highly  ductile  and  mal- 
leable.    Color   copper-red,  usually  dark 
Cube  and  Tetra-  and  with  a  dull  luster  on  account  of 

tarnish. 

Tests.  Fuses  at  3  to  a  globule,  which  becomes  covered  with 
an  oxide  coating  on  cooling.  Dissolves  readily  in  nitric  acid,  and 
the  solution  is  colored  a  deep  blue  on  addition  of  ammonium 
hydroxide  in  excess. 


Fig.  213. 

hexahedron 


PLATE  IV. 


Arborescent  Copper,  Lake  Superior. 


PLATINUM  131 

Occurrence.  A  mineral  found  widely  distributed  in  copper  veins, 
but  usually  in  small  amount.  Associated  with  various  copper  min- 
erals, most  commonly  with  the  oxidized  ores,  cuprite,  malachite  and 
azurite.  Ordinarily  is  strictly  a  secondary  mineral  and  is  to  be 
found  only  in  the  upper  parts  of  copper  veins. 

The  most  notable  deposit  of  native  copper  known  in  the  world 
is  on  Keweenaw  Peninsula  in  northern  Michigan,  on  the  southern 
shore  of  Lake  Superior.  The  region  is  occupied  by  a  series  of  igneous 
flows  of  trap  rock  interbedded  with  sandstone  conglomerates.  The 
whole  series  dips  toward  the  north.  The  copper  is  found  in  veins 
intersecting  this  rock  series;  in  the  amygdaloidal  belts  at  the  top 
of  the  various  trap  flows;  and  as  a  cementing  material  in  the  sand- 
stone conglomerate.  This  last  type  has  furnished  the  most  impor- 
tant ore  deposits,  some  of  which  have  been  worked  for  considerably 
over  a  mile  in  vertical  depth.  -Not  only  does  the  copper  act  as  a  ce- 
ment to  bind  the  conglomerate  together,  but  it  has  often  penetrated 
the  quartz  boulders  of  the  rock  to  a  depth  of  a  foot  or  more.  It  is 
associated  with  such  minerals  as  epidote,  datolite,  calcite  and  various 
zeolites.  The  mines  were  worked  superficially  by  the  Indians,  and 
have  been  actively  developed  since  the  middle  of  the  eighteenth 
century.  Most  of  the  copper  of  the  district  occurs  in  very  small 
irregular  specks,  but  notable  large  masses  have  been  found,  one 
weighing  420  tons  being  discovered  in  1857. 

Sporadic  occurrences  of  copper  similar  to  that  of  the  Lake  Superior 
District  have  been  found  in  the  sandstone  areas  of  the  eastern 
United  States,  notably  in  New  Jersey,  and  in  the  glacial  drift  over- 
lying a  similar  area  in  Connecticut.  Native  copper  occurs  in  small 
amounts,  associated  with  the  oxidized  ores  of  Arizona,  New  Mexico 
and  northern  Mexico. 

Use.  The  most  important  uses  to  which  the  metal  is  put  are 
as  an  electrical  conductor;  in  the  manufacture  of  brass  (an  alloy 
of  copper  and  zinc),  of  bronze  (an  alloy  of  copper  and  tin  with 
frequently  zinc);  for  sheet  copper;  and  as  copper  sulphate, 
which  is  used  in  calico  printing,  in  galvanic  cells,  etc. 

Mercury,  Amalgam  (Ag,Hg)  and  Lead  are  rare  metals. 

PLATINUM-IRON   GROUP. 
Platinum. 

Composition.  Platinum,  usually  alloyed  with  several  per  cent 
of  iron  and  with  smaller  amounts  of  iridium,  osmium,  etc.  The 
amount  of  metallic  platinum  present  seldom  exceeds  80  per  cent. 


132  MANUAL  OF  MINERALOGY 

Crystallization.  Isometric.  Crystals  very  rare.  Commonly 
distorted. 

Structure.  Usually  in  small  grains  or  scales.  Sometimes  in 
irregular  masses  and  nuggets  of  larger  size. 

Physical  Properties.  H.  =  >4.5  (unusually  high  for  a'metal) . 
G.  =  14-19  native;  21-22  when  chemically  pure.  Malleable 
and  ductile.  Color  steel-gray,  with  bright  luster. 

Tests.  B.  B.  infusible.  Unattacked  by  ordinary  reagents; 
soluble  in  a  mixture  of  hydrochloric  and  nitric  acids.  Deter- 
mined by  its  high  specific  gravity,  infusibility  and  insolubility. 


Occurrence.  Platinum  is  a  rare  metal  which  occurs  almost  ex- 
clusively native  (only  one  rare  compound,  sperrylite,  PtAs2,  being 
known).  It  is  found  in  quantity  in  only  a  few  localities,  and  then 
only  in  the  stream  sands,  as  placer  deposits,  where  it  has  been  pre- 
served on  account  of  its  great  weight  and  hardness.  Occurs  in  the 
alluvial  deposits  associated  with  the  rarer  metals  of  the  Platinum 
Group,  gold,  iron-nickel  alloys,  chromite,  etc.  Its  original  source 
is  probably  usually  in  peridotite  rocks  or  the  serpentine  rocks  re- 
sulting from  their  metamorphism.  It  occurs  so  sparingly  dissemi- 
nated through  such  rocks,  however,  that  it  is  only  after  their  disin- 
tegration and  the  subsequent  concentration  of  the  platinum  in  the 
resulting  sands  that  workable  deposits  of  the  metal  are  formed. 
Placer  deposits  of  platinum  are  therefore  to  be  looked  for  in  the 
vicinity  of  masses  of  such  peridotite  rocks. 

Practically  the  entire  world's  supply  of  platinum  at  present  comes 
from  the  Ural  Mountains  in  Russia.  The  central  and  northern  end 
of  this  range  has  large  masses  of  altered  peridotite  rocks,  and  in  the 
sands  of  the  streams  descending  from  it,  chiefly  on  the  eastern  slope 
in  Siberia,  platinum  is  found  in  considerable  quantity.  The  chief 
districts  are  Nizhni  Tagilsk,  Bissersk  and  Goroblagodat,  and  far- 
ther to  the  north,  Bogoslowsk. 

Platinum  was  first  discovered  in  the  United  States  of  Colombia, 
South  America,  where  it  received  its  name  platina  from  plata  (silver) . 
It  is  to  be  found  there  in  two  districts  near  the  Pacific  coast.  The 
chief  district  covers  the  greater  part  of  the  intendencia  of  Choco, 
while  the  second,  that  of  Barbacoas,  is  in  the  department  of  Cauca. 
The  platinum  occurs  here  with  gold  in  placer  deposits,  and,  while 
the  fields  are  not  largely  productive  at  present,  they  may  become  so. 

The  only  platinum  found  in  the  United  States  comes  from  the 
gold  placer  deposits  of  Oregon  and  California,  but  the  yearly  yield 
amounts  to  only  a  few  thousand  dollars  in  value. 


SULPHIDES  133 

Use.  The  uses  of  the  metal  depend  chiefly  upon  its  insolu- 
bility, infusibility  and  superior  hardness.  It  is  used  for  various 
scientific  instruments  such  as  crucibles,  dishes,  etc.,  in  the  chemi- 
cal laboratory;  to  line  the  distilling  apparatus  in  the  manufac- 
ture of  sulphuric  acid;  in  the  electrical  industry  for  contacts, 
etc.;  in  jewelry,  chiefly  as  the  setting  for  diamonds;  as  anodes 
in  the  electrolytic  chemical  industry;  for  electric  heating  appa- 
ratus; for  the  measurement  of  high  temperatures  by  the  use  of 
thermoelectricity;  for  sparking  plugs  in  explosive  motors;  in 
incandescent  electric  lights;  in  the  manufacture  of  false  teeth 
and  in  fillings  for  teeth;  and  in  various  chemical  reactions  which 
are  facilitated  by  the  use  of  finely  divided  platinum. 

Iron. 

Native  iron,  with  always  some  nickel  and  usually  small  amounts 
of  cobalt  and  frequently  traces  of  copper,  manganese,  sulphur,  car- 
bon, phosphorus,  etc.  Isometric.  Practically  always  massive. 
H.  =  4-5.  G.  =  7.3-7.8.  Malleable.  Metallic  luster.  Color  steel- 
gray  to  black.  Strongly  magnetic.  Occurs  very  sparingly  as  terres- 
trial iron,  and  in  the  form  of  meteorites.  Found,  included  in  basalt, 
on  the  west  coast  of  Greenland,  varying  in  size  from  small  dissemi- 
nated grains  to  large  masses.  Has  been  noted  in  a  few  other  locali- 
ties with  a  similar  association.  Nickel-iron  alloys  have  been  found 
in  the  gold  sands  of  New  Zealand  (awaruite),  from  Josephine  County, 
Oregon  (josephinite) ,  and  from  the  Fraser  River,  British  Columbia 
(souesite).  Most  meteorites  contain  native  iron.  The  metal  some- 
times forms  practically  the  entire  body  of  the  meteorite,  while  at 
other  times  it  forms  a  cellular  mass,  inclosing  grains  of  chrysolite,  etc. 
In  the  stony  meteorites,  iron  is  found  disseminated  through  them 
in  the  shape  of  small  grains.  Meteorites  are  to  be  recognized  usually 
by  their  fused  and  pitted  exterior.  At  first  they  are  coated  with  a 
film  of  iron  oxide,  which  disappears,  however,  on  continued  exposure 
to  the  weather. 

Indium,  Iridosmine,  an  alloy  of  iridium  and  osmium,  and 
Palladium  are  rare  metals  in  the  Platinum-Iron  Group. 

SULPHIDES. 

The  sulphides  form  an  important  gi*oup  of  minerals  which  in- 
cludes the  majority  of  the  ore  minerals.  With  them  are  classed 
the  similar  but  rarer  selenides,  tellurides,  arsenides  and  anti- 


134 


MANUAL  OF  MINERALOGY 


monides.  The  sulphides  may  be  divided  into  two  groups  de- 
pending upon  the  character  of  the  metal  present:  (1)  Sulphides 
of  the  Semimetals,  (2)  Sulphides  of  the  Metals. 

SULPHIDES  OF  THE  SEMIMETALS. 

Realgar. 

Composition.  Arsenic  monosulphide,  AsS  =  Sulphur  19.9, 
arsenic  70. 1. 

Crystallization.     Monoclinic.     Short  prismatic  crystals,  ver- 
tically striated.     (See  Fig.  214.) 

Structure.  In  crystals,  coarse  to  fine  granu- 
lar, often  earthy  and  as  an  incrustation. 

Physical  Properties.  Cleavage  parallel  to 
clinopinacoid.  H.  =  1.5-2.  G.  =  3.55.  Resin- 
ous luster.  Color  and  streak  red  to  orange. 
Transparent  to  opaque. 

Tests.  Fusible  at  1.  Easily  volatile.  Heated 
on  charcoal  yields  a  volatile  white  sublimate  of 
arsenious  oxide  with  characteristic  garlic  odor. 
Roasted  in  0.  T.  gives  volatile,  crystalline  subli- 
mate of  arsenious  oxide  and  odor  of  sulphur  dioxide.  Charac- 
terized chiefly  by  deep  red  color  and  resinous  luster. 

Occurrence.  A  rare  mineral,  occurring  usually  with  orpiment, 
As2S3.  Found  associated  with  silver  and  lead  ores  in  Hungary, 
Bohemia,  Saxony,  etc.  Found  in  good  crystals  at  Nagyag,  Tran- 
sylvania; Binnenthal,  Switzerland;  Allchar,  Macedonia.  Occurs 
in  Iron  County,  Utah.  Found  deposited  from  the  geyser  waters  in 
Yellowstone  Park. 

Name.  The  name  is  derived  from  the  Arabic,  Rahj  al  ghar, 
powder  of  the  mine. 

Use.  Was  used  in  fireworks  to  give  a  brillant  white  light  when 
mixed  with  saltpeter  and  ignited.  Artificial  arsenic  sulphide  is 
at  present  used  for  this  purpose. 

Orpiment. 

Composition.  Arsenic  trisulphide,  As2Sa  =  Sulphur  39,  arse- 
nic 61. 


Fig.  214. 


STIBNITE  135 

Crystallization.  Monoclinic.  Crystals  small  and  rarely  dis- 
tinct. 

Structure.     Usually  foliated. 

Physical  Properties.  Very  perfect  cleavage  parallel  to  clino- 
pinacoid.  Folia  flexible  but  not  elastic.  Sectile.  H.  =  1.5-2. 
G.  =  3.4-3.5.  Resinous  luster,  pearly  on  cleavage  face.  Color 
lemon-yellow.  Translucent. 

Tests.  Same  as  for  realgar  (which  see).  Characterized  by 
its  yellow  color,  perfect  cleavage  and  foliated  structure. 

Occurrence.  A  rare  mineral,  associated  usually  with  realgar. 
Found  in  various  places  in  Hungary;  in  Kurdistan;  in  Peru,  etc. 
Occurs  at  Mercur,  Utah.  Deposited  from  geyser  waters  in  the 
Yellowstone  Park. 

Name.   Derived  from  the  Latin,  auripigmentum,  "golden  paint." 
Use.     For  a  pigment,  in  dyeing  and  in  a  preparation  for  the 

removal  of  hair  from  skins.    Artificial  arsenic  sulphide  is  largely 

used  in  place  of  the  mineral. 

Stibnite. 

Composition.  Antimony  trisulphide,  Sb2S3  =  Sulphur  28.6, 
antimony  71.4.  Sometimes  carries  gold  or  silver. 

Crystallization.  Orthorhombic.  Slender  prismatic  habit, 
prism  zone  vertically  striated.  Crystals  often  steeply  termi- 
nated. (See  Fig.  216.)  Often  in  radiating  groups.  Crystals 
sometimes  curved  or  bent  (Fig.  215). 

Structure.  In  radiating  crystal  groups  or  in  bladed  forms  with 
prominent  cleavage.  Massive,  coarse  to  fine  columnar. 

Physical  Properties.  Perfect  cleavage  parallel  to  brachy- 
pinacoid.  H.  =2.  G.  =  4.55.  Metallic  luster,  splendent  on 
cleavage  surfaces.  Color  and  streak  lead-gray. 

Tests.  Very  easily  fusible  at  1.  B.  B.  on  charcoal  gives  dense 
white  coating  of  antimony  trioxide  and  odor  of  sulphur  dioxide. 
When  roasted  in  0.  T.  gives  nonvolatile  white  sublimate  on 
bottom  of  tube  and  a  white  volatile  sublimate  as  ring  around 
tube.  Heated  in  C.  T.  gives  a  faint  ring  of  sulphur  and  below 
a  red  (when  cold)  deposit  of  oxysulphide  of  antimony.  Char- 


136 


MANUAL  OF  MINERALOGY 


acterized  by  its  bladed  structure,  perfect  cleavage  in  one  direc- 
tion, its  lead-gray  color  and  soft  black  streak. 


Fig.  215. 


Fig.  216. 


Occurrence.  Deposited  by  alkaline  waters  in  connection  usually 
with  quartz.  Found  in  quartz  veins  or  beds  in  granite  and  gneiss. 
Associated  with  other  antimony  minerals,  as  the  products  of  its 
decomposition,  and  with  galena,  cinnabar,  sphalerite,  barite  and 
sometimes  gold.  Found  in  various  mining  districts  in  Saxony,  and 
Bohemia,  Mexico,  New  South  Wales,  China,  etc.  Occurs  in  mag- 
nificent crystals  in  Province  of  lyo,  island  of  Shikoku,  Japan. 
Found  in  quantity  only  sparingly  in  the  United  States,  the  chief 
deposits  being  in  California,  Nevada  and  Idaho. 

Use.  Used  in  various  alloys,  as  type  metal,  pewter  and  anti- 
friction metal.  The  sulphide  is  employed  in  the  manufacture 
of  fireworks,  matches,  percussion  caps,  etc.  Used  in  vulcanizing 
rubber.  Used  in  medicine  as  tartar  emetic  and  other  compounds. 
Antimony  trioxide  is  used  as  a  pigment  and  for  making  glass. 


Composition, 
muth  81.2. 

Crystallization. 


Bismuthinite. 

Bismuth  trisulphide,  Bi2S3  =  Sulphur  18.8,  bis- 

Orthorhombic.     In  acicular  crystals. 


MOLYBDENITE  137 

Structure.     Usually  massive,  foliated  or  bladed. 

Physical  Properties.  Perfect  cleavage  parallel  to  brachy- 
pinacoid.  H.  =  2.  G.  =  6.4-6.5.  Metallic  luster.  Color  and 
streak  lead-gray. 

Tests.  Easily  fusible  (1).  Roasted  in  0.  T.  or  B.  B.  on  char- 
coal gives  odor  of  sulphur  dioxide.  Mixed  with  potassium  iodide 
and  sulphur  and  heated  on  charcoal  gives  characteristic  yellow 
to  red  coating.  Resembles  stibnite;  recognized  by  the  test  for 
bismuth. 

Occurrence.  A  rare  mineral,  found  in  Cumberland,  England;  in 
Saxony,  Sweden,  Bolivia,  Beaver  County  in  Utah,  etc. 

Use.    An  ore  of  bismuth.     See  under  native  bismuth. 

Molybdenite. 

Composition.  Molybdenum  disulphide,  MoS2  =  Sulphur  40, 
molybdenum  60. 

Crystallization.  Hexagonal.  Crystals  in  hexagonal-shaped 
plates  or  short,  slightly  tapering  prisms. 

Structure.     Commonly  foliated  massive  or  in  scales. 

Physical  Properties.  Perfect  basal  cleavage.  Laminae  flex- 
ible but  not  elastic.  Sectile.  H  =  1.  G.  =  4.75.  Greasy  feel. 
Metallic  luster.  Color  lead-gray.  Grayish  black  streak. 

Tests.  Infusible.  Heated  B.  B.  gives  yellowish  green  flame. 
Roasted  in  0.  T.  gives  odor  of  sulphur  dioxide  and  deposit  of 
thin  plates  of  molybdenum  oxide,  crossing  the  tube  above  the 
mineral.  Heated  on  charcoal  in  0.  F.  gives  a  white  coating  of 
molybdenum  oxide;  when  this  coating  is  touched  with  R.  F. 
turns  to  deep  blue  color.  Resembles  graphite  but  is  distin- 
guished from  it  by  having  a  blue  tone  to  color,  while  graphite 
has  a  brown  tinge,  and  by  its  reactions  for  sulphur  and  molyb- 
denum. 

Occurrence.  Occurs  in  granite,  gneiss  and  granular  limestone, 
either  as  nests  or  disseminated  through  the  rock.  Found  in  the 
United  States  in  many  localities,  but  usually  not  in  commercial  quan- 
tity. Found  at  Blue  Hill  and  Cooper,  Maine;  Westmoreland,  New 
Hampshire;  Pitkin,  Colorado;  in  Okanogan  County,  Washington. 

Use.    An  ore  of  molybdenum.    See  under  wulfenite. 


138  MANUAL  OF  MINERALOGY 


SULPHIDES,   ETC.,    OF   THE   METALS. 

The  sulphides  of  the  metals  are  divided  into  the  following 
groups:  A.  Basic  Division;  B.  Monosulphide  Division;  C.  In- 
termediate Division;  D.  Disulphide  Division. 


A.  BASIC  DIVISION. 

This  division  includes  several  rare  compounds  of  silver  or  cop- 
per with  antimony  or  arsenic  such  as  dyscrasite,  Ag3Sb  to  Ag6Sb; 
domeykite,  Cu3As;  algodonite,  Cu6As;  whitneyite, 


B.   MONOSULPHIDE  DIVISION. 

1.   GALENA   GROUP.     ISOMETRIC. 

Argentite.     Silver  Glance. 

Composition.  Silver  sulphide,  Ag2S  =  Sulphur  12.9,  silver 
87.1. 

Crystallization.  Isometric.  Cube,  dodecahedron  and  octa- 
hedron the  most  common  forms.  Crystals  often  distorted  and 
arranged  in  branching  or  reticulated  groups. 

Structure.  Commonly  massive,  platy,  earthy  or  as  a  coating. 
More  rarely  in  crystals. 

Physical  Properties.  H.  =  2-2.5.  G.  =  7.3.  Easily  sectile, 
can  be  cut  with  a  knife  like  lead.  Metallic  luster.  Color  and 
streak  blackish  lead-gray.  Streak  shining.  Bright  on  fresh 
surface  but  on  exposure  becomes  dull  black,  due  to  the  forma- 
tion of  an  earthy  sulphide. 

Tests.  Easily  fusible  at  1.5  with  intumescence.  When  fused 
alone  on  charcoal  in  0.  F.  gives  off  odor  of  sulphur  dioxide  and 
yields  a  globule  of  pure  silver.  Distinguished  by  these  tests 
and  by  its  color,  sectility  and  high  specific  gravity. 

Occurrence.  A  fairly  common  ore  of  silver.  Usually  found  in 
silver  veins  as  small  masses,  often  earthy  or  as  a  coating.  Associated 
with  native  silver,  the  ruby  silvers,  stephanite  and  other  silver  min- 
erals; also  galena.  In  the  United  States  it  was  an  important  ore 
in  the  mines  of  the  Comstock  Lode,  Nevada;  at  present  found  in 
Nevada  at  Tonopah  and  elsewhere.  Found  also  in  some  of  the  silver 


GALENA 


139 


districts  of  Arizona.  An  important  ore  in  the  silver  mines  of  Guan- 
ajuato and  elsewhere  in  Mexico;  in  Peru,  Chile  and  Bolivia.  Im- 
portant European  localities  for  its  occurrence  are  Freiberg  in  Saxony, 
Annaberg  in  Austria,  Joachimsthal  in  Bohemia,  Schemnitz  and 
Kremnitz  in  Hungary,  Kongsberg  in  Norway. 

Use.     An  important  ore  of  silver. 

Galena.     Galenite. 

Composition.  Lead  sulphide,  PbS  =  Sulphur  13.4,  lead  86.6. 
Almost  always  carries  traces  of  silver  sulphide,  frequently  enough 
to  make  it  a  valuable  silver  ore.  At  times  also  contains  small 
amounts  of  selenium,  zinc,  •  cadmium,  antimony,  bismuth  and 
copper. 

Crystallization.  Isometric.  Most  common  form  is  the  cube, 
octahedron  sometimes  as  truncations  to  cube,  more  rarely  as  the 


Fig.  217. 
Cube. 


Fig.  218. 
Cube  and  Octahedron. 


•      Fig.  219. 
Octahedron  and  Cube. 


simple  form  (Figs.  217,  218  and  219;  see  also  A,  pl.V.).  Dode- 
cahedron and  trisoctahedron  rare. 

Structure.  Commonly  crystallized  or  massive  cleavable; 
coarse  or  fine  granular. 

Physical  Properties.  Perfect  cubic  cleavage,  H.  =  2.5-2.75.' 
G.  =  7.4-7.6.  Bright  metallic  luster.  Color  and  streak  lead- 
gray. 

Tests.  Easily  fusible  at  2.  Reduced  on  charcoal  to  lead 
globule  with  formation  of  yellow  to  white  coating  of  lead  oxide. 
When  heated  rapidly  in  the  0.  F.  the  coating  is  heavier  and  con- 
sists chiefly  of  a  white  volatile  combination  of  oxides  of  lead  and 
sulphur,  which  resembles  the  antimony  oxide  coating.  Odor  of 
sulphur  dioxide  when  roasted  on  charcoal  or  in  0.  T.  When 


140  MANUAL  OF  MINERALOGY 

treated  with  strong  nitric  acid  is  oxidized  to  white  lead  sulphate. 
Determined  chiefly  by  its  high  specific  gravity,  softness,]  black 
streak  and  cubic  cleavage. 

Alteration.  By  oxidation  it  is  converted  into  the  sulphate, 
anglesite,  the  carbonate,  cerussite,  or  other  compounds. 

Occurrence.  A  very  common  metallic  sulphide,  associated  with 
sphalerite,  pyrite,  marcasite,  chalcopyrite,  cerussite,  anglesite,  dolo- 
mite, calcite,  quartz,  barite,  fluorite,  etc.  Frequently  found  with 
silver  minerals,  often  containing  that  metal  itself  and  so  becoming 
an  important  silver  ore.  A  large  part  of  the  supply  of  lead  comes 
as  a  secondary  production  from  ores  mined  chiefly  for  their  silver. 
Occurs  most  commonly  in  connection  with  limestones,  either  as 
veins  or  irregular  deposits,  or  as  replacement  deposits. 

The  following  are  the  important  lead  producing  localities  in  the 
United  States:  Southeastern  Missouri,  in  which  the  ore  occurs  in 
the  form  of  beds  with  the  mineral  disseminated  through  the  lime- 
stone; southwestern  Missouri,  where  it  is  associated  with  zinc  ores, 
and  is  found  in  irregular  veins  and  pockets  in  limestone  and  chert; 
Idaho,  where  the  lead  is  derived  chiefly  from  lead-silver  deposits, 
the  greater  part  of  which  come  from  near  Wallace  in  Shoshone 
County;  Utah,  in  connection  with  the  silver  deposits  of  the  Tintic 
and  Park  City  districts;  Colorado,  chiefly  from  the  lead-silver  ores 
of  the  Leadville  District. 

The  most  famous  foreign  localities  are,  Freiberg,  Saxony;  the 
Harz  Mountains;  Pfibram,  Bohemia;  Cornwall,  Derbyshire  and 
Cumberland,  England. 

Name.  The  name  galena  is  derived  from  the  Latin  galena,  a 
name  originally  given  to  lead  ore. 

Use.  Practically  the  only  source  of  lead  and  an  important 
ore  of  silver.  Metallic  lead  is  used  chiefly  as  follows:  for  con- 
version into  white  lead  (a  basic  lead  carbonate),  which  is  the 
principal  ingredient  of  the  best  white  paints,  or  into  the  oxides 
used  in  making  glass  and  in  giving  a  glaze  to  earthernware;  as 
pipe  and  sheets;  for  shot;  it  is  one  of  the  ingredients  of  solder 
(an  alloy  of  lead  and  tin),  of  type  metal  (an  alloy  of  lead  and 
antimony)  and  of  low-fusion  alloys  consisting  of  lead,  bismuth 
and  tin. 

The  following  rare  tellurides  belong  in  this  "group;  hessite, 
Ag2Te;  petzite  (Ag,Au)2Te;  dtaite,  PbTe. 


PLATE  V. 


A.    Galena  with  Dolomite,  Joplin,  Missouri. 


B.    Fluorite,  Cumberland,  England. 


CHALCOCITE 


141 


2.   CHALCOCITE   GROUP.     ORTHORHOMBIC. 

Chalcocite.     Copper  Glance. 

Composition.  Cuprous  sulphide,  Cu2S  =  Sulphur  20.2,  cop- 
per 79.8. 

Crystallization.  Orthorhombic.  Usually  in  small  tabular 
crystals  with  hexagonal  outline.  Striated  parallel  to  the  brachy- 


Fig.  220. 


Fig.  221. 


axis  (Fig.  220).  Often  twinned  in  pseudohexagonal  forms  (Fig. 
221). 

Structure.     Massive.     Crystals  very  rare. 

Physical  Properties.  Conchoidal  fracture.  H.  =  2.5-3.  G. 
=  5.5-5.8.  Metallic  luster.  Color  shining  lead-gray,  tarnish- 
ing on  exposure  to  dull  black.  Streak  grayish  black. 

Tests.  Easily  fusible  at  2-2.5.  In  0.  T.  or  B.  B.  on  charcoal 
gives  odor  of  sulphur  dioxide.  Roasted  mineral,  moistened  with 
hydrochloric  acid,  gives  azure-blue  flame.  Soluble  in  nitric  acid; 
and  the  solution  with  an  excess  of  ammonia  turns  dark  blue. 
Recognized  by  its  massive  structure,  its  high  specific  gravity, 
its  color,  softness  and  black  streak. 

Occurrence.  Found  in  crystals  in  Cornwall,  England,  and  Bris- 
tol, Connecticut.  Occurs  as  a  mineral  of  secondary  origin  in  the  en- 
riched zone  of  copper  veins  associated  with  bornite,  chalcopyrite, 
enargite,  malachite,  pyrite,  etc.  Found  as  an  ore  at  Monte  Catini, 
Tuscany;  Mexico,  Peru,  Bolivia,  Chile,  etc.  Occurs  in  immense 


142 


MANUAL  OF  MINERALOGY 


deposits   at   Butte,    Montana.     Found   in   Alaska   at   Kennecott, 
Copper  River  District. 

Use.    An  important  copper  ore. 

Stromeyerite. 

A  sulphide  of  silver  and  copper  (Ag,Cu)2S  or  Ag2S.Cu2S.  Ortho- 
rhombic.  Commonly  massive.  H.  =  2.5-3.  G.=  6.15-6.3.  Me- 
tallic luster.  Color  and  streak  grayish  black.  Fusible  at  1.5.  In 
O.  T.  gives  odor  of  sulphur  dioxide.  Roasted  mineral  with  hydro- 
chloric acid  gives  azure-blue  flame.  Nitric  acid  solution  with  hydro- 
chloric acid  gives  precipitate  of  silver  chloride.  A  rare  silver  mineral 
found  with  other  silver  ores. 

3.   SPHALERITE   GROUP.     ISOMETRIC,    TETRAHEDRAL. 
Sphalerite.     Zinc  Blende,  Black  Jack. 

Composition.  Zinc  sulphide,  ZnS  =  Sulphur  33,  zinc  67.  Al- 
most always  contains  at  least  a  small  percentage  of  iron  replac- 
ing the  zinc,  but  the  amount  of  iron  may  rise  as  high  as  15  to 
18  per  cent.  Also  frequently  contains  small  amounts  of  manga- 
nese, cadmium,  mercury,  etc. 

Crystallization.  Isometric;  tetrahedral.  Tetrahedron  (Fig. 
222),  dodecahedron  and  cube  common  forms,  but  the  crystals 


Fig.  222. 


Fig.  223. 


frequently  highly  complex  and  usually  distorted  or  in  rounded 
forms.    Often  twinned. 

Structure.     Usually  massive  cleavable,  coarse  to  fine  granular. 
Compact,  botryoidal.    Also  in  rounded  crystal  masses. 


SPHALERITE  143 

Physical  Properties.  Perfect  dodecahedral  cleavage.  H.  = 
3.5-4.  G.  =  4-4.1.  Nonmetallic  and  resinous  to  submetallic 
luster;  also  adamantine.  Color  white  when  pure,'  and  green 
when  nearly  so.  Commonly  yellow,  brown  to  black,  darkening 
with  increase  in  the  amount  of  iron  present.  Transparent  to 
translucent.  Streak  white  to  yellow  and  brown. 

Tests.  Infusible  with  pure  zinc  sulphide  to  difficultly  fusible 
with  increase  in  amount  of  iron.  Gives  odor  of  sulphur  dioxide 
when  heated  on  charcoal  or  in  0.  T.  Decomposed  in  powder  by 
warm  hydrochloric  acid  with  evolution  of  hydrogen  sulphide  gas, 
which  may  be  detected  by  its  disagreeable  odor.  When  heated 
on  charcoal  gives  a  coating  of  zinc  oxide  (yellow  when  hot,  white 
when  cold)  which  is  nonvolatile  in  oxidizing  flame.  Recognized 
usually  by  its  striking  resinous  luster  and  perfect  cleavage.  The 
dark  varieties  (black  jack)  can  be  told  by  noting  that  a  knife 
scratch  leaves  a  reddish  brown  streak. 

Occurrence.  Sphalerite,  the  most  important  ore  of  zinc,  is  an 
extremely  common  mineral,  especially  as  a  constituent  of  metallic 
veins.  Found  widely  distributed,  but  chiefly  in  veins  and  irregular 
bodies  in  limestone  rocks.  Associated  with  galena,  pyrite,  marcasite, 
chalcopyrite,  smithsonite,  calcite,  dolomite,  siderite,  etc.  May  carry 
silver  or  gold.  Large  deposits  are  found  in  the  United  States  in 
Missouri,  Kansas,  Arkansas,  Wisconsin,  Iowa,  Illinois,  Colorado. 
The  chief  locality  for  its  production  is  the  Joplin  District  in  south- 
western Missouri.  Found  in  large  quantities  in  connection  with  the 
lead-silver  deposits  of  Leadville,  Colorado.  Noteworthy  European 
localities  are  at  Alston  Moor  and  other  places  in  the  lead-mining  dis- 
tricts of  northern  England;  Binnenthal,  Switzerland,  in  fine  crystals; 
at  Schemnitz  and  other  localities  in  the  gold  and  silver-mining  dis- 
tricts of  Hungary. 

Name.  The  name  blende  is  from  the  German,  blind  or  decep- 
tive, because  while  often  resembling  galena  it  yielded  no  lead. 
Sphalerite,  for  the  same  reason,  is  derived  from  a  Greek  word 
meaning  treacherous. 

Use.  The  most  important  ore  of  zinc.  The  chief  uses  for 
metallic  zinc,  or  spelter,  are  in  galvanizing  iron,  making  brass, 
an  alloy  of  copper  and  zinc,  in  electric  batteries,  and  as  sheet 
zinc.  Zinc  oxide,  or  zinc  white,  is  used  extensively  for  making 


144  MANUAL  OF  MINERALOGY 

paint.  Zinc  chloride  is  used  as  a  preservative  for  wood.  Zinc 
sulphate  is  used  in  dyeing  and  in  medicine.  Sphalerite  also 
serves  as  the  most  important  source  of  cadmium. 

Alabandite. 

Manganese  sulphide,  MnS.  Isometric;  tetrahedral.  Usually  gran- 
ular massive.  Cubic  cleavage.  H.  =  3.5-4.  G.  =  3.95.  Subme- 
tallic  luster.  Color  iron-black,  tarnished  to  brown  on  exposure. 
Streak  olive-green.  Fusible  at  3.  Gives  odor  of  sulphur  dioxide 
when  roasted  in  O.T.  Soluble  in  hydrochloric  acid  with  evolution 
of  hydrogen  sulphide  gas.  With  sodium  carbonate  in  O.  F.  gives 
opaque  greenish  blue  bead  (manganese).  A  rare  mineral,  occurring 
usually  with  gold  or  silver  ores. 

Pentlandite. 

A  sulphide  of  iron  and  nickel  (Ni,Fe)S.  Isometric.  Massive 
granular.  Octahedral  cleavage.  H.  =  3.5-4.  G.  =  4.55-5.  Metal- 
lic luster.  Yellowish  bronze  color.  Black  streak.  Fusible  at  1.5-2. 
Gives  odor  of  sulphur  dioxide  in  O.  T.  Magnetic  on  heating  in 
R.  F.  Roasted  mineral  in  O.  F.  colors  borax  bead  reddish  brown 
(nickel).  Closely  resembles  pyrrhotite  in  appearance  but  to  be 
distinguished  by  the  octahedral  cleavage.  A  rare  mineral,  found 
with  chalcopyrite  near  Lillehammer,  Norway,  and  with  pyrrhotite 
and  chalcopyrite  in  the  nickel  deposits  at  Sudbury,  Canada. 

Other  minerals  which  are  rare  in  occurrence  that  belong  in 
this  group  are,  metacinnabarite,  HgS;  tiemannite,  HgSe;  onofrite, 
Hg(S,Se);  coloradoite,  HgTe. 


4.   CINNABAR-MILLERITE   GROUP.     HEXAGONAL. 
Cinnabar. 

Composition.  Mercuric  sulphide,  HgS  =  Sulphur  13.8,  mer- 
cury 86.2.  Usually  impure  from  admixture  of  clay,  iron  oxide, 
etc. 

Crystallization.  Hexagonal-rhombohedral;  trapezohedral. 
Crystals  usually  rhombodedral,  often  in  penetration  twins. 
Trapezohedral  faces  rare. 

Structure.  Usually  fine  granular  massive;  also  earthy  and 
as  incrustations.  Crystals  rare. 


COVELLITE  145 

Physical  Properties.  H.  =  2-2.5.  G.  =  8.10.  Adamantine 
luster  when  pure,  to  dull  and  earthy  when  impure.  Color  ver- 
milion-red when  pure,  to  brownish  red  when  impure.  Scarlet 
streak.  Transparent  to  opaque. 

Tests.  Wholly  volatile  when  free  from  gangue.  Gives  black 
sublimate  of  mercury  sulphide  when  heated  alone  in  C.  T. 
When  carefully  heated  in  C.  T.  with  dry  sodium  carbonate  gives 
globules  of  metallic  mercury.  Carefully  roasted  in  0.  T.  gives 
odor  of  sulphur  dioxide  and  sublimate  of  metallic  mercury. 
Recognized  usually  by  color,  streak  and  high  specific  gravity. 

Occurrence.  The  most  important  ore  of  mercury,  but  found  in 
quantity  at  comparatively  few  localities.  Occurs  filling  fissures, 
cavities,  etc.,  usually  in  sedimentary  rocks;  frequently  as  impregna- 
tions in  sandstone  or  limestone.  Associated  with  pyrite,  marcasite, 
sulphur,  calcite,  barite,  gypsum,  opal,  quartz,  etc.  Always  found 
in  the  neighborhood  of  igneous  rock  masses  from  which  it  is  thought 
that  the  mercury  was  derived.  Deposited  probably  through  the 
agency  of  ascending  hot  waters.  Deposits  of  mercuric  sulphide  are 
being'  formed  to-day  by  the  hot  springs  at  Steamboat  Springs,  Ne- 
vada, and  at  Ohaiawai,  New  Zealand.  The  important  localities  for 
the  occurrence  of  cinnabar  are  at  Almaden,  Spain;  Idria  in  Carniola; 
Huancavelica  in  southern  Peru;  Kwei  Chaw,  China;  New  Idria  in 
San  Benito  County,  Napa  County,  and  New  Almaden  in  Santa  Clara 
County,  California;  Terlingua,  Brewster  County,  Texas.  Hepatic 
cinnabar  is  an  inflammable  variety  with  liver-brown  color  and  some- 
times a  brownish  streak,  usually  granular  or  compact. 

Name.    The  name  cinnabar  is  supposed  to  have  come  from 
India,  where  it  is  applied  to  a  red  resin. 
Use.     The  only  important  source  of  mercury. 

Covellite. 

Cupric  sulphide,  CuS.  Hexagonal.  Rarely  in  tabular  hexagonal 
crystals  with  prominent  basal  plane.  Usually  massive.  Perfect 
basal  cleavage.  H.  =  1.5-2.  G.  =  4.59.  Metallic  luster.  Color 
indigo-blue.  Fusible  at  2.5.  Gives  odor  of  sulphur  dioxide  in 
O.  T.  and  much  sulphur  in  C.  T.  The  roasted  mineral,  moistened 
with  hydrochloric  acid  and  ignited,  gives  a  blue  flame  (copper). 
When  moistened  with  water  shows  a  strong  purple  color.  A  rare 
mineral,  found  only  in  the  enriched  sulphide  zone  of  copper  deposits, 
associated  with  chalcocite,  bornite,  etc. 


146  MANUAL  OF  MINERALOGY 

Greenockite. 

Composition.  Cadmium  sulphide,  CdS  =  Sulphur  22.3,  cad- 
mium 77.7. 

Crystallization.  Hexagonal;  hemimorphic.  Crystals  hemi- 
morphic,  showing  prism  faces  and  terminated  usually  below  with 
base  and  above  with  pyramids. 

Structure.  Usually  pulverulent,  as  thin  powdery  incrusta- 
tions. Crystals  small  and  rare. 

Physical  Properties.  H.  =  3-3.5.  G.  =  4.9-5.  Luster  ada- 
mantine to  resinous,  earthy.  Color  yellow. 

Tests.  Infusible.  Yields  odor  of  sulphur  dioxide  when 
heated  B.  B.  or  in  0.  T.  Decomposed  by  hydrochloric  acid 
with  the  evolution  of  hydrogen  sulphide  gas,  which  may  be  de- 
tected by  its  disagreeable  odor.  Gives  a  reddish  brown  coating 
of  cadmium  oxide  when  heated  with  sodium  carbonate  on  char- 
coal. Characterized  by  its  yellow  color  and  pulverulent  form. 

Occurrence.  Most  common  mineral  containing  cadmium  but 
found  only  in  a  few  localities  and  in  small  amount.  Associated 
usually  with  zinc  ores,  often  as  a  coating  on  sphalerite  and  smith- 
sonite.  Found  in  crystals  at  Bishopton,  Renfrewshire,  Scotland; 
with  the  zinc  ores  of  southwestern  Missouri  and  in  Arkansas,  also 
in  various  localities  in  Bohemia  and  Greece. 

Use.  A  source  of  cadmium.  Cadmium-bearing  zinc  ores  fur- 
nish the  greater  part  of  the  metal  produced.  Cadmium  is  used 
in  alloys  for  dental  and  other  purposes.  The  sulphide  serves  as 
a  yellow  pigment. 

Millerite.     Capillary  Pyrites. 

Composition.  Nickel  sulphide,  NiS  =  Sulphur  35.3,  nickel 
64.7. 

Crystallization.     Hexagonal-rhombohedral. 

Structure.  Usually  in  hairlike  tufts  and  radiating  groups  of 
slender  to  capillary  crystals.  Sometimes  in  velvety  incrusta- 
tions. 

Physical  Properties.  Cleavage  rhombohedral.  H.  =  3-3.5. 
G.  =  5.65.  Metallic  luster.  Pale  brass-yellow;  with  a  green- 


PYRRHOTITE  147 

ish  tinge  when  in  fine  hairlike  masses.    Streak  black,  somewhat 
greenish. 

Tests.  'Fusible  at  1.5-2  to  magnetic  globules.  Gives  odor 
of  sulphur  dioxide  when  heated  on  charcoal  or  in  0.  T.  The 
roasted  mineral  colors  the  borax  bead  reddish  brown  in  0.  F. 

Occurrence.  Occurs  in  various  localities  in  Saxony  and  Bohemia; 
in  Cornwall;  with  hematite  and  siderite  at  Antwerp,  N.  Y.;  with 
pyrrhotite  at  the  Gap  Mine,  Lancaster  County,  Pennsylvania;  in 
calcite  at  St.  Louis,  Missouri,  Keokuk,  Iowa,  etc. 

Use.     A  subordinate  ore  of  nickel. 

Niccolite.     Copper  Nickel. 

Composition.  Nickel  arsenide,  NiAs  =  Arsenic  56.1,  nickel 
43.9.  Usually  with  a  little  iron,  cobalt  and  sulphur.  Arsenic 
frequently  replaced  in  part  by  antimony. 

Crystallization.     Hexagonal;  hemimorphic  (?). 

Structure.     Usually  massive.     Crystals  rare. 

Physical  Properties.  H.  =  5-5.5.  G.  =  7.5.  Metallic  lus- 
ter. Color  pale  copper-red,  (hence  called  copper-nickel)  with 
gray  to  blackish  tarnish.  Brownish  black  streak. 

Tests.  Fusible  (2).  When  heated  B.  B.  on  charcoal  a  white 
volatile  deposit  of  arsenious  oxide  forms  and  a  garlic-like  odor 
is  given  off.  Gives  to  borax  bead  a  reddish  brown  color  (nickel). 
Characterized  chiefly  by  its  color. 

Occurrence.  Associated  usually  with  cobalt,  silver  and  copper 
minerals.  Not  very  common.  Found  in  the  silver  mines  of  Saxony, 
in  Sweden,  at  Cobalt,  Canada,  etc. 

Use.    A  minor  ore  of  nickel. 

Pyrrhotite.     Magnetic  Pyrites. 

Composition.  A  sulphide  of  iron,  varying  in  composition  from 
Fe6S6  up  to  FeieSn.  FenSi2  is  the  usually  accepted  formula. 
Often  carries  a  small  amount  of  nickel. 

Crystallization.  Hexagonal.  Crystals  usually  tabular,  or 
sometimes  pyramidal. 


148  MANUAL  OF  MINERALOGY 

Structure.  Practically  always  massive  with  granular  or  lamel- 
lar structure. 

Physical  Properties.  H.  =  4.  G.  =  4.65.  Metallic  luster. 
Brownish  bronze  color.  Black  streak.  Usually  slightly  mag- 
netic, but  sometimes  scarcely  at  all  so. 

Tests.  Easily  fusible.  Strongly  magnetic  after  heating. 
B.»  B.  or  in  0.  T.  gives  odor  of  sulphur  dioxide.  Little  or  no 
sulphur  in  C.  T.  Decomposed  by  hydrochloric  acid,  giving  off 
hydrogen  sulphide  gas.  Recognized  usually  by  its  massive 
structure  and  bronze  color. 

Occurrence.  A  common  minor  constituent  of  igneous  rocks. 
Occurs  in  large  masses  in  intimate  association  with  basic  igneous 
rocks  and  is  thought  by  many  to  have  been  formed  through  mag- 
matic  differentiation.  This  view  is  doubted  by  many  and  is  still 
open  to  question.  Associated  with  the  ferromagnesian  minerals  of 
the  rocks  in  which  it  occurs,  and  also  with  chalcopyrite,  and  nickel 
minerals,  as  pentlandite,  millerite,  etc.  Found  in  large  quantities 
in  Norway  and  Sweden,  at  Sudbury,  Ontario,  Canada;  at  Stafford 
and  Ely,  Vermont;  at  Ducktown,  Tennessee.  Was  found  at  the 
Gap  Mine,  Lancaster  County,  Pennsylvania. 

Name.     Derived  from  a  Greek  word  meaning  reddish. 
Use.    Serves  as  an  important  ore  of  nickel,  particularly  at 
Sudbury,  Ontario. 

In  this  group  belongs  also  the  rare  mineral,  wurtzite,  ZnS,  which 
differs  from  sphalerite,  since  it  is  Hexagonal  in  crystallization. 

C.  INTERMEDIATE  DIVISION. 
Bornite.     Purple  Copper  Ore,  etc. 

Composition.  Cu5FeS4  =  Sulphur  25.5,  copper  63.3,  iron 
11.2.  Analyses  of  different  specimens  show  quite  a  wide  varia- 
tion in  the  percentages  of  the  elements  present,  copper  ranging 
from  55  to  71  per  cent.  Analyses  of  the  purest  material,  how- 
ever, agree  with  the  above  formula. 

Crystallization.  Isometric.  Crystals  rare.  Usually  in  rough 
cubes,  sometimes  in  penetration  twins.  Dodecahedron  and  octa- 
hedron at  times. 

Structure.    Commonly  massive. 


LINNMITE  149 

Physical  Properties.  H.  =  3.  G.  =  4.9-5.4.  Metallic  lus- 
ter. Color  brownish  bronze  on  fresh  fracture  but  quickly  tar- 
nishing on  exposure  to  variegated  purple  and  blue  and  finally  to 
almost  black.  Streak  grayish  black. 

Tests.  Easily  fusible  at  2.5.  Gives  odor  of  sulphur  dioxide 
on  charcoal  or  in  0.  T.  Yields  only  a  very  little  sulphur  in  C.  T. 
Becomes  magnetic  in  R.  F.  If,  after  roasting,  it  is  moistened 
with  hydrochloric  acid  and  heated,  it  gives  an  azure-blue  flame 
(copper).  Easily  soluble  in  nitric  acid  with  separation  of  sul- 
phur; solution  neutralized  with  ammonia  gives  red-brown  pre- 
cipitate of  ferric  hydroxide  and  blue  color  to  filtrate.  Charac- 
terized chiefly  by  its  purple  tarnish. 

Occurrence.  An  important  and  widely  occurring  ore  of  copper, 
but  usually  with  other  copper  minerals  and  in  subordinate  amount. 
It  has  been  found  as  a  primary  constituent  in  igneous  rocks  and  in 
pegmatite  veins.  Bornite  and  chalcopyrite  are  the  two  common 
original  copper  minerals,  from  which  other  copper  minerals  have 
been  derived  through  secondary  action.  It  is  also  frequently,  itself, 
a  secondary  mineral,  formed  in  the  upper,  enriched  zone  of  copper 
veins  through  the  action  of  descending  copper-bearing  solutions, 
upon  chalcopyrite.  The  minerals  with  which  it  is  commonly  asso- 
ciated are  chalcopyrite,  chalcocite,  enargite,  malachite,  azurite, 
pyrite,  etc.  It  frequently  occurs  in  intimate  mixture  with  chal- 
copyrite and  chalcocite.  Found  in  the  United  States  at  Butte, 
Montana;  in  the  copper  mines  of  Virginia  and  North  Carolina.  It 
was  found  in  unusual  crystals,  associated  with  crystallized  chalcocite 
at  Bristol,  Connecticut.  Occurs  at  Acton,.  Canada.  Found  in 
Cornwall;  Monte  Catini,  Tuscany,  and  in  various  other  European 
countries.  An  important  ore  in  Chile,  Peru,  Bolivia  and  Mexico. 

Name.  Bornite  was  named  after  the  mineralogist  von  Born 
(1742-1791).  Sometimes  called  horseflesh  ore  in  reference  to 
the  color  on  the  fresh  fracture,  or  variegated  copper  ore  or  peacock 
ore  because  of  its  purple  tarnish.  Called  for  the  latter  reason 
erubescite  by  English  mineralogists. 

Use.    An  important  ore  of  copper. 

Linnagite. 

A  sulphide  of  cobalt,  Co3S4  or  CoS.Co2S3,  with  the  cobalt  replaced 
in  varying  amount  by  nickel.  Isometric.  In  small  octahedral 


150  MANUAL  OF  MINERALOGY 

crystals  or  granular  massive.  H.  =  5.5.  G.  =  4.9.  Metallic  lus- 
ter. Color  pale  steel-gray.  Grayish  black  streak.  Fusible  at  2. 
Gives  odor  of  sulphur  dioxide  in  O.  T.  Fuses  in  R.  F.  to  a  magnetic 
globule.  Roasted  mineral  colors  the  borax  bead  blue  (cobalt).  A 
rare  mineral,  found  with  chalcopyrite  near  Riddarhyttan,  Sweden; 
with  barite  and  siderite  at  Miisen,  Prussia;  with  lead  ores  at  Mine  La 
Motte,  Missouri. 


Chalcopyrite.     Copper  Pyrites.     Yellow  Copper  Ore. 

Composition.  A  sulphide  of  copper  and  iron,  CuFeS2  =  Sul- 
phur 35,  copper  34.5,  iron  30.5. 

Crystallization.  Tetragonal;  sphenoidal.  Crystals  usually  in 
unit  sphenoids  (Fig.  224),  which  because  the  vertical  axis  is  close 
to  unity  (c  =  0.985)  are  very  near  to  the  isometric  tetrahedron 


Fig.  224.  Fig.  225. 

in  angles.  Steeper  sphenoids  (Fig.  225),  and  other  more  complex 
forms  occasionally  observed. 

Structure.     Usually  massive,  compact;   at  times  in  crystals. 

Physical  Properties.  H.  =  3.5.  G.  =  4.2-4.3.  Metallic  lus- 
ter. Color  brass-yellow;  often  tarnished  to  bronze  or  iridescent. 
Streak  greenish  black. 

Tests.  Easily  fusible  to  a  magnetic  globule.  Gives  odor  of 
sulphur  dioxide  when  heated  B.  B.  or  in  O.  T.  Gives  sulphur  in 
C.  T.  After  roasting,  and  moistening  with  hydrochloric  acid, 
gives  an  azure-blue  flame.  Readily  decomposed  by  nitric  acid, 
giving  separated  sulphur;  solution  made  ammoniacal  gives  red- 
brown  precipitate  of  ferric  hydroxide  and  blue  filtrate  (copper). 
Recognized  by  its  brass-yellow  color,  greenish  black  streak  and 
its  softness.  Distinguished  from  pyrite  by  its  being  softer  than 


PYRITE  151 

steel  and  from  gold  by  its  being  brittle.     Known  sometimes  as 
"fool's  gold/'  a  term  which  is  also  applied  at  times  to  pyrite. 

Occurrence.  The  most  common  ore  of  copper.  Occurs  widely 
distributed  in  metallic  veins  associated  with  pyrite,  pyrrhotite, 
bornite,  chalcocite,  tetrahedrite,  malachite,  azurite,  sphalerite, 
galena,  quartz,  calcite,  dolomite,  siderite,  etc.  May  carry  gold  or 
silver  and  become  an  ore  of  those  metals.  Often  in  subordinate 
amount  with  large  bodies  of  pyrite,  making  them  serve  as  low-grade 
copper  ores.  Chief  ore  of  copper  mines  at  Cornwall,  England; 
Falun,  Sweden;  Rio  Tinto,  Spain;  Sudbury,  Canada;  in  South 
Africa,  Chile,  etc.  Found  widely  in  the  United  States  but  usually 
in  connection  with  other  copper  minerals  in  equal  or  greater  amount; 
found  at  Butte,  Montana;  Bingham,  Utah;  various  districts  in 
California,  Colorado,  Arizona,  etc. 

Name.  Derived  from  Greek  word  meaning  brass  and  from 
pyrites. 

Use.     Most  important  ore  of  copper. 

Stannite. 

A  sulphide  of  copper,  tin  and  iron,  Cu2S.FeS.SnS2.  Zinc  at 
times  also  present.  Tetragonal,  sphenoidal,  but  pseudo-isometric 
through  twinning.  Practically  always  massive.  H.  =  4.  G.  =  4.4. 
Metallic  luster.  Color  steel-gray.  Streak  black.  Fusible  at  1.5. 
Slightly  magnetic  after  heating  in  R.  F.  After  roasting,  and  moist- 
ening with  hydrochloric  acid,  gives  when  ignited  a  blue  flame  (cop- 
per). Fused  alone  on  charcoal  gives  a  nonvolatile  white  coating 
of  tin  oxide.  A  rare  mineral,  found  in  various  places  in  Cornwall 
and  with  the  tin  ores  of  Bolivia. 


D.   BISULPHIDE  DIVISION. 
1.  PYRITE  GROUP.     ISOMETRIC;  PYRITOHEDRAL. 

Pyrite.     Iron  Pyrites. 

Composition.  Iron  disulphide,  FeS2  =  Sulphur  53.4,  iron  46.6. 
Sometimes  contains  small  amounts  of  nickel,  cobalt  and  copper. 
Frequently  carries  minute  quantities  of  gold  (auriferous  pyrite) . 

Crystallization.  Isometric;  pyritohedral.  Most  common 
crystal  forms  are  the  cube,  the  faces  of  which  are  usually  striated, 
the  striae  on  adjacent  faces  being  perpendicular  to  each  other 


152 


MANUAL  OF  MINERALOGY 


(Fig.  226) ;  the  octahedron,  and  the  pentagonal  dodecahedron, 
known  commonly  as  the  pyritohedron  (Fig.  227).     Figs.  228  to 


Fig.  226.    Striated  Cubes. 


Fig.  227.    Pfyritohedron 


Fig.  228. 

Cube 
and  Pyritohedron. 


Fig.  229. 
Octahedron 
and  Pyritohedron. 


Fig.  230. 

Octahedron 

and  Pyritohedron. 


230  show  characteristic  combinations  of  these  forms.  Fig.  231 
shows  a  penetration  twin  that  is  at 
times  observed. 

Structure.  Often  in  crystals.  Also 
massive,  granular,  reniform,  globular 
and  stalactitic. 

Physical  Properties.  Brittle. 
H.  =  6-6.5  (unusually  hard  for  a  sul- 
phide). G.  =  4.95-5.10.  Luster  me- 
tallic, splendent.  Color  pale  brass- 
yellow,  becoming  darker  at  times  on 
Streak  greenish  or  brownish  black. 


Fig.  231.    Twinned 
Pyritohedrons. 

account  of  tarnish. 


PYRITE  153 

Tests.  Easily  fusible  (2.5-3)  to  a  magnetic  globule.  Yields 
much  sulphur  in  C.  T.  Gives  off  sulphur  dioxide  in  0.  T.  or 
B.  B.  on  charcoal.  Insoluble  in  hydrochloric  acid.  Fine  pow- 
der completely  soluble  in  nitric  acid,  but  may  yield  separated 
sulphur  when  too  rapidly  decomposed.  Distinguished  from 
chalcopyrite  by  its  paler  color  and  the  fact  that  it  cannot  be 
scratched  by  steel;  from  gold  by  its  being  brittle. 

Occurrence.  Pyrite  is  the  most  common  of  the  sulphides.  It  is 
a  common  vein  mineral,  occurring  in  rocks  of  all  ages  and  associated 
with  many  different  minerals.  Found  frequently  with  chalcopyrite, 
sphalerite,  galena,  etc.  Is  widely  distributed  as  an  accessory  rock 
mineral  in  both  igneous  and  sedimentary  rocks.  Important  de- 
posits of  pyrite  in  the  United  States  are  in  Prince  William,  Louisa 
and  Pulaski  counties,  Virginia,  where  it  occurs  in  large  lenticular 
masses  which  conform  in  position  to  the  foliation  of  the  inclosing 
schists;  in  St.  Lawrence  County,  New  York;  at  the  Davis  Mine, 
near  Charlemont,  Massachusetts;  in  various  places  in  California. 
Largo  deposits  occur  at  Rio  Tinto  and  other  mines  in  Spain,  also  in 
Portugal. 

Alteration.  Pyrite  is  easily  altered  to  oxides  of  iron,  usually 
limonite.  It  is,  however,  in  general  much  more  stable  than 
marcasite.  Pseudomorphic  crystals  of  limonite  after  pyrite  are 
common.  Pyrite  veins  are  usually  capped  by  a  cellular  deposit 
of  limonite,  termed  gossan.  Rocks  that  contain  pyrite  are  un- 
suitable for  structural  purposes  because  the  ready  oxidation  of 
the  pyrite  in  them  would  serve  both  to  disintegrate  the  rock 
and  to  stain  it  with  iron  oxide. 

Name.  The  name  pyrite  is  from  a  Greek  word  meaning  fire, 
in  allusion  to  the  fact  that  when  struck  with  steel  it  gives  off 
brilliant  sparks. 

Use.  Pyrite  is  often  mined  for  the  gold  or  copper  associated 
with  it.  Because  of  the  large  amount  of  sulphur  present  in  the 
mineral  it  is  never  used  as  an  iron  ore.  It  is  chiefly  used  to  fur- 
nish sulphuric  acid  and  copperas  (ferrous  sulphate).  Sulphuric 
acid  is  perhaps  the  most  important  of  all  chemicals,  being  used 
for  many  different  purposes,  some  of  the  more  important  being 
in  the  purification  of  kerosene  and  in  the  preparation  of  mineral 
fertilizers.  The  gas  S02  derived  either  through  burning  sulphur 


154  MANUAL  OF  MINERALOGY 

or  by  roasting  pyrite  is  used  extensively  in  the  preparation  of 
wood  pulp  for  manufacture  into  paper.  Copperas  is  used  in 
dyeing,  in  the  manufacture  of  inks,  as  a  preservative  of  wood, 
and  for  a  disinfectant. 

Smaltite-Chloanthite. 

Smaltite  is  cobalt  arsenide,  CoAs2;  chloanthite,  nickel  arsenide, 
NiAs2.  The  two  molecules  are  isomorphous  and  all  gradations 
between  the  two  species  occur.  Isometric;  pyritohedral.  Usually 
massive,  granular.  Octahedral  cleavage.  H.  =  5.5-6.  G.  =  6.3- 
6.8.  Metallic  luster.  Color  tin-white.  Streak  black.  Fusible  at 
2-2.5.  Roasted  on  charcoal  give  a  volatile  coating  of  arsenious 
oxide  with  characteristic  garlic  odor.  In  borax  bead  in  O.  F.  give 
blue  color  (cobalt).  Rare  species,  occurring  with  other  cobalt  and 
nickel  minerals,  often  associated  with  silver  and  copper  ores. 

Cobaltite-Gersdorffite. 

Cobaltite  is  a  sulpharsenide  of  cobalt,  CoAsS;  gersdorffite  a 
sulpharsenide  of  nickel,  NiAsS.  The  two  molecules  are  isomor- 
phous with  each  other,  and  may  occur  together  in  varying  amounts. 
Usually,  however,  any  specimen  will  be  found  to  be  near  one  or  the 
other  ends  of  the  series.  Iron  is  frequently  present,  replacing  the 
cobalt  or  the  nickel,  and  sometimes  in  considerable  amount.  Iso- 
metric; pyritohedral.  Cobaltite  commonly  in  cubes,  pyritohedrons 
and  octahedrons,  also  massive.  Gersdorffite  usually  massive.  Cubic 
cleavage.  H.  =  5.5-6.  G.  =  5.8-6.2.  Metallic  luster.  Color,  tin- 
white,  in  cobaltite  inclining  to  reddish  tone.  Streak  black.  Fusible 
2-3.  On  charcoal  give  a  volatile  white  sublimate  of  arsenious  oxide 
with  characteristic  garlic  odor.  In  O.  T.  give  volatile  crystalline 
sublimate  of  arsenious  oxide  with  odor  of  sulphur  dioxide.  In  O.  F. 
in  borax  bead  give  deep  blue  color  (cobalt) ;  if  gersdorffite  contains 
no  cobalt,  gives  brown  bead  (nickel).  Rare  minerals,  cobaltite 
being  the  commoner.  Found  associated  with  other  cobalt  and 
nickel  minerals  and  with  silver  and  copper  ores.  Notable  occur- 
rences of  cobaltite  are  at  Tunaberg,  Sweden,  and  Cobalt,  Ontario, 
Canada. 

Sperrylite. 

A  platinum  arsenide,  PtAs2.  Isometric;  pyritohedral.  Usually 
in  small  grains,  or  in  almost  microscopic  crystal  fragments.  H.  = 
6-7.  G.  =  10.6.  Metallic  luster.  Tin-white  color.  Black  streak. 
Fusible  at  2.  Roasted  on  charcoal  gives  volatile  white  coating  of 


MARCASITE  155 

arsenious  oxide  with  characteristic  garlic  odor.  Roasted  in  O.  T., 
at  first  very  gently,  a  platinum  sponge  is  left,  which  is  insoluble  in 
any  single  acid.  A  very  rare  mineral  and  the  only  known  compound 
of  platinum  occurring  in  nature.  Found  with  chalcopyrite  in  a 
gold-quartz  vein  near  Sudbury,  Canada,  and  with  covellite  at  the 
Rambler  Mine,  Encampment,  Wyoming. 

2.  MARCASITE   GROUP.    ORTHORHOMBIC. 
Marcasite.     White  Iron  Pyrites. 

Composition.  Iron  disulphide,  like  pyrite,  FeS2  =  Sulphur 
53.4,  iron  46.6. 

Crystallization.  Orthorhombic.  Crystals  commonly  tabular 
parallel  to  basal  plane,  showing  also  short  prisms  and  low  brachy- 
domes  (Fig.  232).  The  brachydomes  usually  striated  parallel 


Fig.  232.  Fig.  233. 

to  the  brachy-axis.  Often  twinned,  giving  coxcomb  and  spear- 
shaped  groups  (Fig.  233).  Closely  related  in  crystal  forms  and 
habit  to  arsenopyrite. 

Structure.  Usually  in  radiating  forms.  Often  stalactitic, 
having  an  inner  core  with  radiating  structure  and  covered  on  the 
outside  with  irregular  crystal  groups.  Also  globular,  reniform, 
etc.  More  rarely  in  crystals. 

Physical  Properties.  H.  =  6-6.5.  G.  =  4.85-4.9.  Metallic 
luster.  Color  pale  yellow  to  almost  white,  yellow  to  brown  tar- 
nish. Streak  grayish  black. 

Tests.  Fusible  (2.5-3)  to  a  magnetic  globule.  B.  B.  on  char- 
coal or  in  0.  T.  gives  odor  of  sulphur  dioxide.  Much  sulphur  in 


156  'MANUAL  OF  MINERALOGY 

C.  T.  When  fine  powder  is  treated  by  cold  nitric  acid,  and  the 
solution  allowed  to  stand  until  vigorous  action  ceases  and  then 
boiled,  the  mineral  is  decomposed  with  separation  of  sulphur. 
Pyrite  treated  in  the  same  manner  would  have  been  completely 
dissolved.  Recognized  usually  by  its  pale  yellow  color,  its  crys- 
tals or  its  fibrous  structure. 

Occurrence.  Marcasite  is  found  in  metalliferous  veins,  frequently 
with  lead  and  zinc  ores.  Also  at  times  in  sedimentary  rocks.  It 
is  more  unstable  than  pyrite,  being  easily  decomposed,  and  is  not 
nearly  as  common  in  its  occurrence.  Found  abundantly  in  clay 
near  Carlsbad  and  elsewhere  in  Bohemia;  in  various  places  in 
Saxony;  in  the  chalk  marl  of  Folkestone  and  Dover,  England;  with 
zinc  and  lead  deposits  of  Joplin,  Missouri,  and  of  Mineral  Point, 
Wisconsin. 

Name.    Derived  from  an  Arabic  word,  at  one  time  applied 
generally  to  pyrite. 
Use.    To  a  slight  extent  as  a  source  of  sulphuric  acid,  etc. 

Arsenopyrite.     Mispickel. 

Composition.  Sulpharsenide  of  iron,  FeAsS  =  Arsenic  46, 
sulphur  19.7,  iron  34.3.  Sometimes  cobalt  replaces  a  part  of  the 
iron  (danaite). 

Crystallization.  Orthorhombic.  Usually  in  tabular  diamond- 
shaped  crystals,  formed  by  a  short  prism  terminated  by  low 
brachydomes.  The  brachydomes  are  usually  striated  parallel 


Fig.  234.  Fig.  235. 

to  the  brachy-axis  (Fig.  234).     Twinned  at  times,  giving  stellate 
groups;   the  different  individuals  of  the  twin  groups  being  dis- 


SYLVANITE  157 

tinguished  from  each  other  by  the  direction  of  the  striations 
upon  them  (Fig.  235).  Agrees  closely  in  angles  and  crystal  habit 
with  marcasite. 

Structure.     In  crystals.     Massive,  granular  to  compact. 

Physical  Properties.  H.  =  5.5-6.  G.  =  6-6.2.  Metallic  lus- 
ter. Silver-white  color.  Black  streak. 

Tests.  Fusible  at  2  to  a  magnetic  globule.  B.  B.  on  charcoal 
gives  a  volatile  coating  of  arsenious  oxide  and  a  characteristic 
garlic  odor.  In  0.  T.  gives  odor  of  sulphur  dioxide  and  a  volatile 
ring  of  arsenious  oxide.  In  C.  T.  gives  arsenic  mirror.  Recog- 
nized usually  by  its  silver-white  color,  its  crystals  and  a  test  for 
arsenic. 

Occurrence.  Arsenopyrite  is  the  most  common  mineral  contain- 
ing arsenic.  Found  in  veins  in  crystalline  rocks,  associated  with 
ores  of  tin,  silver,  lead  and  with  pyrite,  chalcopyrite,  sphalerite,  etc. 
Sometimes  it  is  auriferous  and  serves  as  a  gold  ore.  Occurs  in  quan- 
tity at  Freiberg  and  Munzig,  Saxony;  in  the  Harz  Mountains;  with 
tin  ores  in  Cornwall,  England;  in  various  places  in  Bolivia;  New 
South  Wales;  Deloro,  Canada,  where  it  is  mined  as  a  gold  ore;  Rox- 
bury,  Connecticut,  etc. 

Use.  An  ore  of  arsenic.  Arsenious  oxide  is  used  in  the  manu- 
facture of  glass,  as  a  poison  and  a  preservative.  Paris  green,  an 
arsenate  and  acetate  of  copper,  is  used  as  a  poison  and  a  pigment. 
Sulphides  of  arsenic  are  used  for  paints  and  fireworks. 

3.   SYLVANITE   GROUP. 

Sylvanite. 

Composition.  Telluride  of  gold  and  silver  (Au,Ag)Te2.  The 
ratio  of  the  amounts  of  gold  and  silver  varies  somewhat;  when 
Au  :  Ag  =  1  :  1  =  Tellurium  62.1,  gold  24.5,  silver  13.4. 

Crystallization.     Monoclinic.     Distinct  crystals  rare. 

Structure.  Usually  bladed  or  granular.  Often  in  skeleton 
forms  deposited  on  rock  surfaces  and  resembling  writing  in 
appearance. 

Physical  Properties.  Perfect  cleavage  parallel  to  clinopina- 
coid.  H.  =1.5-2.  G.  =8-8.2.  Brilliant  metallic  luster.  Color 
silver-white.  Streak  gray. 


158  MANUAL  OF  MINERALOGY 

Tests.  Easily  fusible  (1).  If  a  little  of  the  powdered  mineral 
is  heated  in  concentrated  sulphuric  acid  the  solution  assumes  a 
deep  red  color  (tellurium).  When  decomposed  in  nitric  acid 
leaves  a  rusty-colored,  spongy  mass  of  gold,  and  the  solution 
with  hydrochloric  acid  gives  white  precipitate  of  silver  chloride. 
With  sodium  carbonate  on  charcoal  gives  a  globule  of  gold  and 
silver.  Determined,  by  above  tests,  by  its  silver  color  and  good 
cleavage. 

Occurrence.  A  rare  mineral,  found  with  gold  ores  at  Offenbdnya 
and  Nagydg  in  Transylvania;  Kalgoorlie,  West  Australia;  Cripple 
Creek,  Colorado. 

Name.     Derived  from  Transylvania,  where  it  was  first  found. 
Use.     An  ore  of  gold. 

Calaverite. 

Composition.  Gold  telluride,  AuTe2  =  Tellurium  55.97,  gold 
44.03.  Silver  usually  present  isomorphous  with  the  gold,  to  a 
small  extent. 

Crystallization.  Monoclinic.  Crystals  usually  developed 
parallel  to  the  ortho-axis  and  the  faces  of  the  orthodome  zone 
deeply  striated.  Terminated  at  the  ends  of  the  ortho-axis  with 
a  large  number  of  faces.  Crystallization  complicated.  Twin- 
ning frequent. 

Structure.     Usually  granular.     Distinct  crystals  rare. 

Physical  Properties.  H.  =  2.5.  G.  =  9.35.  Metallic  luster. 
Silver-white  color,  sometimes  with  yellowish  tarnish.  Streak 
gray. 

Tests.  Easily  fusible  (1).  If  a  little  of  the  powdered  mineral 
is  heated  in  concentrated  sulphuric  acid  the  solution  assumes  a 
deep  red  color  (tellurium).  When  decomposed  by  nitric  acid 
leaves  a  rusty-colored,  spongy  mass  of  gold,  and  on  addition  of 
hydrochloric  acid  gives  only  a  slight  precipitate  of  silver  chloride. 
Distinguished  from  sylvanite  by  small  amount  of  silver  present 
and  by  its  lack  of  a  cleavage. 

Occurrence.  Found  with  sylvanite  and  other  tellurides  in  the 
Cripple  Creek  District,  Colorado,  and  at  Kalgoorlie,  West  Australia. 


JAMESONITE  159 

Name.     Found  originally  at  the  Stanislaus  Mine,  Calaveras 
County,  California,  whence  name. 
Use.     An  ore  of  gold. 

Other  rare  tellurides  belonging  to  this  group  are,  krennerite, 
AuTe2,  and  nagyagite,  a  sulpho-telluride  of  lead  and  gold. 


SULPHARSENITES,   ETC. 

The  minerals  in  this  division  are  considered  to  be  salts  of  the 
sulpho-acids  of  trivalent  arsenic,  antimony  and  bismuth.  Vari- 
ous types  of  these  acids  are  found,  such  as  H3AsS3,  H2AsS2, 
13^8285,  etc.  A  subdivision  includes  the  sulpharsenates,  etc., 
being  chiefly  salts  of  the  acid  H3AsS4.  The  metals  observed  are 
most  commonly  copper,  silver  and  lead;  also  at  times  iron,  zinc 
and  mercury. 

Jamesonite.     Feather  Ore. 

Composition.  Sulphantimonite  of  lead,  Pb3Sb2S6  or 
3PbS.Sb2S3  =  Sulphur  19.7,  antimony  29.5,  lead  50.8. 

Crystallization.     Orthorhombic. 

Structure.  Usually  in  acicular  crystals  or  in  capillary  forms. 
Also  fibrous  to  compact  massive. 

Physical  Properties.  Basal  cleavage.  Brittle.  H.  =  2-3. 
G.  =  5.5-6.  Metallic  luster.  Color  and  streak  steel-gray  to 
grayish  black. 

Tests.  Fusible  at  1.  On  charcoal  gives  a  combination  coat- 
ing of  lead  and  antimony  oxides.  Roasted  in  0.  T.  gives  sub- 
limates of  antimony  oxides.  Heated  on  charcoal  with  a  mixture 
of  potassium  iodide  and  sulphur  gives  a  chrome-yellow  coating 
of  lead  iodide.  Recognized  by  above  tests  and  characteristic 
fibrous  structure.  Difficult  to  distinguish  from  similar  species 
(see  below). 

Occurrence.  Found  in  Cornwall,  England,  and  from  various 
localities  in  Hungary,  Saxony,  etc.;  from  Bolivia.  Noted  in  the 
United  States  from  Sevier  County,  Arkansas,  and  the  Montezuma 
Mine,  Nevada. 


160  MANUAL  OF  MINERALOGY 

Similar  Species.  There  are  a  number  of  minerals  similar 
to  jamesonite  in  composition  and  general  physical  charac- 
teristics whose  relations  to  each  other  in  many  cases  are  not 
thoroughly  understood.  These  include  such  minerals  as  zinken- 
ite,  PbS.Sb2S3;  plagionite,  5PbS.4Sb2S3;  warrenite,  3PbS.2Sb2S3; 
boulangerite,  3PbS.Sb2S3;  meneghinite,  4PbS.Sb2S3;  geocronite, 
5PbS.Sb2S3. 

Bournonite. 

Composition.  Sulphantimonite  of  lead  and  copper 
(Pb,Cu2)3Sb2S6  or  3(Pb,Cu2)S.Sb2S3.  The  relative  amounts  of 
the  lead  and  copper  present  vary,  but  in  general  correspond 
closely  to  the  ratio,  Pb  :  Cu2  =2:1. 

Crystallization.  Orthorhombic.  Crystals  usually  short  pris- 
matic to  tabular.  Sometimes  quite  complex  with  many  prism, 
pyramid  and  dome  faces.  Frequently 
twinned,  giving  tabular  crystals  with 
recurring  reentrant  angles  in  the  prism 
zone  (Fig.  236),  whence  the  common 
name  of  cogwheel  ore. 

Structure.      Massive;    granular   to 
compact;  in  crystals. 

Physical    Properties.       H.  =  2.5-3. 
Fig.  236.  G.  =  5.7-5.9.     Metallic  luster.     Color 

and  streak  steel-gray  to  black. 

Tests.  Fusible  at  1.  B.  B.  on  charcoal  gives  a  combination 
coating  of  antimony  and  lead  oxides.  Roasted  in  0.  T.  gives 
sublimates  of  antimony  oxides.  Heated  on  charcoal  with  a 
mixture  of  potassium  iodide  and  sulphur  gives  a  chrome-yellow 
coating  of  lead  iodide.  Decomposed  with  nitric  acid,  solution 
turns  blue  with  excess  of  ammonia  (copper).  Recognized  either 
by  characteristic  crystals  or  above  tests. 

Occurrence.  A  rare  mineral.  Found  at  Neudorf  and  other  locali- 
ties in  the  Harz  Mountains;  Kapnik  in  Hungary;  Liskeard  in  Corn- 
wall, etc.  Has  been  found,  also,  in  various  places  in  the  United 
States,  but  not  in  notable  amount  or  quality. 


PROUSTITE  161 

Pyrargyrite.     Dark  Ruby  Silver. 

Composition.  Sulphantimonite  of  silver,  Ag3SbS3  or 
SAgaS.SbaSs  =  Sulphur  17.8,  antimony  22.3,  silver  59.8. 
Sometimes  contains  a  small  amount  of  arsenic.  Compare 
proustite. 

Crystallization.  Hexagonal-rhombohedral ;  hemimorphic. 
Crystals  prismatic  with  rhombohedral  and  scalenohedral  termi- 
nations. Usually  distorted  and  often  with  complex  develop- 
ment. Frequently  twinned. 

Structure.  In  crystals  or  massive;  compact;  in  disseminated 
grains. 

Physical  Properties.  Rhombohedral  cleavage.  H.  =  2.5.  G. 
=  5.85.  Luster  adamantine.  Color  usually  dark  red  to  black, 
in  thin  splinters  deep  ruby-red.  Indian-red  streak. 

Tests.  Fusible  at  1.  On  charcoal  gives  dense  white  coating 
of  antimony  trioxide.  After  prolonged  heating,  coating  becomes 
tinged  with  a  reddish  color  near  assay  due  to  a  small  amount  of 
volatilized  silver.  Odor  of  sulphur  dioxide  and  coatings  of  anti- 
mony oxides  when  heated  in  0.  T.  Decomposed  by  nitric  acid 
and  solution  with  hydrochloric  acid  gives  white  precipitate 
of  silver  chloride.  Characterized  chiefly  by  its  dark  red  color 
and  streak. 

Occurrence.  A  rare  silver  mineral  associated  with  proustite, 
argentite,  galena,  calcite,  etc.  Found  in  the  silver  mines  at  Andreas- 
berg,  Harz  Mountains;  at  Freiberg,  Saxony;  Pfibram,  Bohemia; 
in  Hungary;  Transylvania;  Norway;  in  Guanajuato,  Mexico;  at 
Chanarcillo,  Chile.  Found  in  various  silver  veins  in  the  San  Juan 
Mountains  and  elsewhere  in  Colorado;  in  the  silver  districts  of 
Nevada,  New  Mexico,  etc. 

Name.     Derived  from  two  Greek  words  meaning  fire-silver. 
Use.    An  ore  of  silver. 

Proustite.     Light  Ruby  Silver. 

Composition.  Sulpharsenite  of  silver,  Ag3AsS3  or  3Ag2S.As2S3 
=  Sulphur  19.4,  arsenic  15.2,  silver  65.4.  May  contain  a  small 
amount  of  antimony.  Compare  pyrargyrite. 


162  MANUAL  OF  MINERALOGY 

Crystallization.  Hexagonal-rhombohedral;  hemimorphic. 
Crystals  commonly  with  prominent  steep  rhombohedrons  and 
scalenohedrons.  Often  distorted  and  frequently  complex  in 
development. 

Structure.  Commonly  massive,  compact,  in  disseminated 
grains. 

Physical  Properties.  Rhombohedral  cleavage.  H.  =  2-2.5. 
G.  =  5.55.  Adamantine  luster.  Color  ruby-red.  Transparent 
to  translucent.  Red  streak.  High  index  of  refraction. 

Tests.  Fusible  at  1.  Heated  on  charcoal  gives  volatile  sub- 
limate of  arsenious  oxide  with  characteristic  garlic  odor.  In  O.T. 
gives  odor  of  sulphur  dioxide  and  volatile  crystalline  sublimate 
of  arsenious  oxide.  In  C.  T.  gives  abundant  sublimate  of  arsenic 
sulphide,  reddish  black  when  hot,  reddish  yellow  when  cold. 
With  sodium  carbonate  on  charcoal  gives  a  globule  of  silver. 
Characterized  chiefly  by  its  ruby-red  color  and  streak  and  its 
brilliant  luster. 

Occurrence.  A  rare  mineral,  occurring  in  silver  veins  associated 
with  various  other  sulpharsenites  and  sulphantimonites.  Found  in 
the  silver  mines  of  Saxony;  Bohemia;  at  Chaftarcillo,  Chile,  in  fine 
crystals;  common  in  the  silver  mines  of  Peru  and  Mexico.  Found 
in  Colorado  in  the  silver  mines  of  the  San  Juan  Mountains  and  else- 
where; in  various  silver  districts  in  Nevada,  etc. 

Use.    An  ore  of  silver. 


Tetrahedrite-Tennantite.     Gray  Copper.     Fahlore. 

Composition.  Tetrahedrite,  Cu8Sb2S7  or  4Cu2S.Sb2S3  =  Sul- 
phur 23.1,  antimony  24.8,  copper  52.1.  Tennantite,  Cu8As2S7  or 
4Cu2S.As2S3  =  Sulphur  25.5,  arsenic  17.0,  copper  57.5.  Anti- 
mony and  arsenic  are  usually  both  present  and  the  two  species 
graduate  into  each  other,  so  that  no  sharp  line  can  be  drawn 
between  them.  The  copper  is  often  replaced  in  varying  amounts 
by  iron,  zinc,  silver,  mercury,  lead,  etc. 

Crystallization.  Isometric;  tetrahedral.  Habit  tetrahedral. 
Tetrahedron  (Fig.  237),  tristetrahedron,  dodecahedron  and  cube 
the  common  forms. 


STEPHANITE  163 

Structure.  Frequently  in  crystals.  Also  massive,  coarse  or 
fine  granular. 

Physical  Properties.  H.  =  3-4.  G.  =  4.7-5.  Metallic  lus- 
ter, often  splendent.  Color  grayish  black  to  black.  Streak 
black. 

Tests.  Easily  fusible  at  1.5.  On  charcoal  or  in  O.  T.  gives 
tests  for  antimony  or  arsenic,  or  both.  After  roasting,  and 
moistening  with  hydrochloric  acid,  gives 
azure-blue  flame.  Decomposed  by  nitric 
acid  with  separation  of  sulphur  and  anti- 
mony trioxide;  solution  made  alkaline 
with  ammonia  turns  blue.  The  two 
species  are  only  to  be  told  apart  by  test- 
ing for  the  presence  of  antimony  and 
arsenic,  and  as  both  are  often  present  in  Fig  237 

the  same  specimen  a  quantatitive  analysis 

may  be  necessary  in  order  to  positively  determine  to  which  end 
of  the  series  it  belongs.  Recognized  by  its  tetrahedral  crystals, 
or  when  massive  by  its  fine-grained  structure  and  by  its  gray 
color. 

Occurrence.  Found  in  metallic  veins  usually  associated  with 
chalcopyrite,  pyrite,  sphalerite,  galena  and  various  other  silver,  lead 
and  copper  ores.  May  carry  sufficient  silver  to  become  an  important 
ore  of  that  metal  (the  highly  argentiferous  variety  is  known  as 
freibergite) .  Is  found  in  the  United  States  in  various  silver  and 
copper  mines  in  Colorado,  Nevada,  Arizona,  etc.  Found  in  Corn- 
wall, England;  the  Harz  Mountains,  Germany;  Freiberg,  Saxony; 
Pfibram  in  Bohemia;  various  places  in  Hungary;  in  the  silver  mines 
of  Mexico,  Chile,  Peru  and  Bolivia. 

Use.    An  ore  of  silver  and  copper. 

Stephanite. 

Composition.  Sulphantimonite  of  silver,  Ag6SbS4  or 
5Ag2S.Sb2S3  =  Sulphur  16.3,  antimony  15.2,  silver  68.5. 

Crystallization.  Orthorhombic.  Crystals  usually  short  pris- 
matic and  tabular  parallel  to  the  base.  Edges  of  crystals  trun- 
cated by  various  pyramids.  Prism  zone  usually  shows  the  four 
prism  faces  and  the  two  of  the  brachypinacoid,  all  making 


164  MANUAL  OF  MINERALOGY 

nearly  60°  angles  with  each  other  and  so  giving  the  crystals  a 
hexagonal  aspect.  Also  twinned  in  pseudohexagonal  crystals. 
Crystals  usually  small. 

Structure.     Massive,  in  disseminated  grains;  crystallized. 

Physical  Properties.  H.  =  2-2.5.  G.  =  6.2-6.3.  Metallic 
luster.  Color  and  streak  iron-black. 

Tests.  Fusible  at  1.  B.  B.  on  charcoal  gives  dense  white 
sublimate  of  antimony  trioxide  and  odor  of  sulphur  dioxide. 
Decomposed  by  nitric  acid,  and  if  after  filtering  a  little  hydro- 
chloric acid  is  added  to  filtrate,  it  gives  a  white  precipitate  of 
silver  chloride.  Recognized  by  its  stout  hexagonal  crystals 
and  the  above  tests. 

Occurrence.  A  rare  silver  mineral.  Found  associated  with  other 
sulphantimonites  of  silver,  etc.  Occurs  at  Freiberg  and  other  locali- 
ties in  Saxony;  in  Bohemia  and  Hungary;  at  Guanajuato  and  Arizpe, 
Sonora,  etc.,  Mexico;  in  Peru  and  Chile.  In  the  United  States  was 
an  abundant  ore  at  the  Comstock  Lode  and  other  silver  deposits  in 
Nevada. 

Use.    An  ore  of  silver. 

Polybasite. 

Composition.  Sulphantimonite  of  silver,  Ag9SbS6  or 
9Ag2S.Sb2S3  =  Sulphur  15,  antimony  9.4,  silver  75.6.  Copper  re- 
places a  part  of  the  silver  and  arsenic  replaces  the  antimony. 

Crystallization.  Monoclinic.  Crystals  are  pseudorhombohe- 
dral  in  symmetry,  occurring  in  short  hexagonal  prisms,  often  thin 
tabular.  Basal  planes  show  triangular  markings. 

Structure.     In  crystals.     Granular. 

Physical  Properties.  H.  =  2-3.  G.  =  6-6.2.  Metallic  lus- 
ter. Color  steel-gray  to  iron-black.  Streak  black. 

Tests.  Fusible  at  1.  B.  B.  on  charcoal  gives  dense  white 
coating  of  antimony  trioxide  with  odor  of  sulphur  dioxide.  After 
decomposition  by  nitric  acid,  the  filtrate  with  hydrochloric  acid 
gives  white  precipitate  of  silver  chloride.  To  be  distinguished 
from  other  similar  species  chiefly  by  its  crystals. 

Occurrence.  A  comparatively  rare  silver  mineral,  associated  with 
other  sulphantimonides  of  silver  and  with  silver  ores  in  general. 


CHLORIDES  165 

Found  in  the  silver  mines  of  Mexico,  Chile,  Saxony  and  Bohemia. 
Found  in  the  United  States  at  the  Comstock  Lode,  Nevada;  near 
Ouray,  Colorado,  etc. 

Name.     Name  is  in  allusion  to  the  many  bases  contained  in  the 
mineral. 
Use.    An  ore  of  silver. 

Enargite. 

Composition.  Sulpharsenate  of  copper,  Cu3AsS4  or 
3Cu2S.As2S5  =  Sulphur  32.6,  arsenic  19.1,  copper  48.3.  Anti- 
mony may  replace  in  part  the  arsenic,  and  the  species  graduate 
toward  famatinite  (3Cu2S.Sb2S5). 

Crystallization.  Orthorhombic.  Prismatic  crystals  with 
prism  zone  vertically  striated. 

Structure.     Columnar,  bladed,  massive. 

Physical  Properties.  Perfect  prismatic  cleavage.  H.  =  3. 
G.  =  4.43-4.45.  Metallic  luster.  Color  and  streak  grayish 
black  to  iron-black. 

Tests.  Easily  fusible  (1).  B.  B.  on  charcoal  gives  volatile 
white  sublimate  of  arsenious  oxide  and  characteristic  garlic  odor. 
In  0.  T.  gives  white  crystalline  sublimate  of  arsenious  oxide  and 
odor  of  sulphur  dioxide.  Roasted  on  charcoal,  then  moistened 
with  hydrochloric  acid  and  again  ignited,  gives  azure-blue  flame. 
Characterized  by  its  color,  its  cleavage  and  the  above  tests. 

Occurrence.  A  comparatively  rare  mineral,  found  associated  with 
other  copper  minerals,  as  chalcocite,  bornite,  tennantite,  etc.  Found 
abundantly  at  Morococha,  Peru;  also  in  the  United  States  of  Col- 
ombia; Argentine  Republic;  island  of  Luzon,  Philippines.  Found 
in  considerable  quantity  with  the  copper  ores  at  Butte,  Montana. 
Occurs  in  the  silver  mines  of  the  San  Juan  Mountains,  Colorado. 

Use.  An  ore  of  copper.  Arsenic  oxide  also  obtained  from  it 
at  Butte,  Mont. 

CHLORIDES,   ETC. 

The  chlorides  with  the  related  bromides,  iodides  and  fluorides 
are  grouped  into  the  following  divisions:  (1)  Anhydrous  Chlor- 
ides, etc.;  (2)  Oxychlorides,  etc.;  (3)  Hydrous  Chlorides,  etc. 


166  MANUAL  OF  MINERALOGY 

1.  ANHYDROUS  CHLORIDES,   ETC. 
HALITE   GROUP. 

The  Halite  Group  includes  the  isometric  minerals  halite,  NaCl; 
sylvite,  KC1;  cerargyrite,  AgCl;  embolite,  Ag(Cl,Br);  bromyrite, 
AgBr. 

Halite.     Common  Salt. 

Composition.  Sodium  chloride,  NaCl  =  Chlorine  60.6,  so- 
dium 39.4.  Commonly  contains  impurities,  such  as  calcium 
sulphate  and  calcium  and  magnesium  chlorides. 

Crystallization.  Isometric.  Habit  cubic 
(Fig.  238).  Other  forms  very  rare. 

Structure.  In  crystals  or  granular  crystal- 
line, in  masses  showing  cubical  cleavage, 
known  as  rock  salt.  Also  massive,  granular 
to  compact. 

Physical  Properties.    Perfect  cubic  cleav- 
age.    H.  =  2.5.    G.  =  2.1-2.6.    Transparent 
to  translucent.     Colorless  or  white,  or  when  impure  may  have 
shades  of  yellow,  red,  blue,  purple.     Readily  soluble  in  water. 
Salty  taste.     Diathermous. 

Tests.  Easily  fusible  at  1.5,  giving  strong  yellow  flame  of 
sodium.  After  intense  ignition  B.  B.  residue  gives  alkaline  re- 
action to  moistened  test  paper.  Readily  soluble  in  water; 
solution  made  acid  with  nitric  acid  gives  with  silver  nitrate  a 
heavy  white  precipitate  of  silver  chloride.  Salty  taste.  Dis- 
tinguished from  sylvite  (KC1)  by  its  yellow  flame  color  and  by 
the  latter  having  a  somewhat  more  bitter  taste. 

Occurrence.  A  common  and  widely  disseminated  mineral,  oc- 
curring often  in  extensive  beds  and  irregular  masses,  intersfcratified 
in  rocks  of  all  ages,  in  such  a  manner  as  to  form  a  true  rock  mass. 
Associated  with  gypsum,  sylvite,  anhydrite,  calcite,  clay,  sand,  etc. 
Occurs  also  dissolved  in  the  waters  of  salt  springs,  salt  seas  and  the 
ocean. 

The  deposits  of  salt  have  been  formed  by  the  gradual  evaporation 
and  ultimate  drying  up  of  inclosed  bodies  of  salt  water.  The  salt 


HALITE  167 

beds  formed  in  this  way  have  subsequently  been  covered  by  other 
sedimentary  deposits  and  gradually  buried  beneath  the  rock  strata 
formed  from  them.  The  salt  beds  range  from  a  few  feet  up  to  one 
hundred  in  thickness  and  have  been  found  at  depths  of  two  thousand 
feet  and  more  from  the  surface.  The  history  of  the  formation  of 
these  salt  beds  is  as  follows:  River  waters  contain  a  small  but 
appreciable  amount  of  various  soluble  salts.  When  these  waters 
are  collected  in  a  sea  which  has  no  outlet,  or  in  other  words,  a  sea 
where  the  evaporation  equals  or  exceeds  the  amount  of  water  flowing 
in,  there  is  a  gradual  concentration  in  the  sea  of  the  salts  brought 
into  it  by  the  rivers.  The  sea  water,  therefore,  in  time  becomes 
heavily  charged  with  soluble  salts,  particularly  sodium  chloride. 
When  the  points  of  concentration  of  the  various  salts  held  in  solu- 
tion are  reached,  they  will  be  deposited  progressively  upon  the  sea 
bottom,  commencing  with  the  most  insoluble.  This  process  may 
continue  for  a  long  period  of  time  and  ultimately  a  thick  layer  of 
salt  and  other  soluble  minerals  be  formed  on  the  bottom.  The 
process  may  be  interrupted  by  seasons  of  flood  in  which  the  sea 
water  becomes  freshened  beyond  the  concentration  point.  Silt 
materials  may  be  brought  in  at  such  times  and  deposited  upon  the 
bottom  and  so  form  beds  of  clay  alternating  with -those  of  salt. 
Such  deposits  of  salt  have  been  formed  whenever  favorable  condi- 
tions occurred,  and  are  now  to  be  found  buried  in  rock  strata  of  all 
ages.  At  the  present  time  similar  deposits  are  being  formed  in  the 
Great  Salt  Lake  and  the  Dead  Sea. 

In  the  United  States  salt  is  produced,  on  a  commercial  scale,  in 
some  fifteen  states,  either  from  rock-salt  deposits,  or  by  evaporation 
of  salt  lake  or  sea  waters.  Beds  of  rock  salt  are  found  in  New  York 
State  from  the  Oatka  Valley  in  Wyoming  County  east  to  Morrisville, 
Madison  County,  and  south  of  this  line  wherever  wells  have  been 
driven  deep  enough  to  reach  the  beds.  The  important  producing 
localities  are  near  Syracuse,  Ithaca,  Watkins  and  Ludlowville,  and 
at  various  places  in  Wyoming,  Genesee  and  Livingston  counties. 
Extensive  deposits  of  salt  occur  in  Michigan,  chiefly  in  Saginaw, 
Bay,  Midland,  Isabella,  Detroit,  Wayne,  Manistee,  and  Mason 
counties.  Notable  deposits  are  also  found  in  Ohio,  Kansas,  Louisi- 
ana. Salt  is  obtained  by  the  evaporation  of  saline  waters  in  Cali- 
fornia, Utah  and  Texas. 

Important  foreign  localities  for  the  production  of  salt  are  to  be 
found  in  Austrian  Poland,  Hungary,  Bavaria,  Prussia,  Spain  and 
Great  Britain. 

Use.  The  chief  uses  of  salt  are  for  culinary  and  preserva- 
tive purposes.  It  is  used  also  in  the  manufacture  of  soda  ash 
(sodium  carbonate) ,  which  is  used  in  glass  making,  soap  making, 


168  MANUAL  OF  MINERALOGY 

bleaching,  etc.,  and  in  the  preparation  of  sodium  salts  in  general. 
Salt  is  used  also  in  the  extraction  of  gold  by  the  chlorination 
process. 

Sylvite. 

Composition.  Potassium  chloride,  KC1  =  Chlorine  47.6,  po- 
tassium 52.4.  Sometimes  contains  sodium  chloride. 

Crystallization.    Isometric.     Cube  and  oc- 
tahedron frequently  in  combination  (Fig.  239). 
Structure.     Usually  in  granular  crystalline 
masses  showing  cubic  cleavage;   compact. 

Physical  Properties.     Perfect  cubical  cleav- 
Fig  239  age.     H.  =  2.     G.  =  1.9.     Transparent  when 

pure.  Colorless  or  white;  also  shades  of  blue, 
yellow  or  red  from  impurities.  Readily  soluble  in  water.  Salty 
taste  but  more  bitter  than  in  the  case  of  halite. 

Tests.  Easily  fusible  at  1.5,  giving  violet  flame  of  potassium, 
which  may  be  obscured  by  yellow  flame  due  to  sodium  present. 
The  yellow  sodium  flame  may  be  filtered  out  by  use  of  a  blue 
glass,  and  the  violet  of  the  potassium  rendered  visible.  After 
intense  ignition,  residue  gives  alkaline  reaction  on  moistened 
test  paper.  Readily  soluble  in  water;  solution  made  acid  with 
nitric  acid  gives  with  silver  nitrate  a  heavy  precipitate  of  silver 
chloride.  Distinguished  from  halite  by  the  violet  flame  color  of 
potassium  and  its  slightly  bitter  taste. 

Occurrence.  Has  the  same  origin,  mode  of  occurrence  and  asso- 
ciations as  halite  (which  see)  but  is  much  more  rare.  Found  in 
some  quantity  and  at  times  well  crystallized  in  connection  with  the 
salt  deposits  at  Stassfurt,  Prussia. 

Name.  Potassium  chloride  is  the  sal  digestivus  Sylvii  of  early 
chemistry,  whence  the  name  for  the  species. 

Use.  One  source  of  potassium  compounds  which  are  exten- 
sively used  as  fertilizers.  Other  potassium  minerals  that  are 
found  in  Germany  in  sufficient  amount  to  make  them  valuable 
as  sources  of  potassium  salts  are,  carnallite,  KCl.MgCl2.6H20 
(see  page  173);  kainite,  MgS04.KC1.3H20;  polyhalite, 
K2S04.MgS04.2CaS04.2H20. 


EMBOLITE  169 

Cerargyrite.     Horn  Silver. 

Composition.  Silver  chloride,  AgCl  =  Silver  75.3,  chlorine 
24.7.  Some  varieties  contain  mercury. 

Crystallization.     Isometric.     Habit  cubic. 

Structure.  Usually  massive,  resembling  wax;  often  in  plates 
and  crusts. 

Physical  Properties.  H.  =  2-3.  G.  =  5.8-6.  Sectile,  can  be 
cut  with  a  knife  like  horn.  Transparent  to  translucent.  Color 
pearl-gray  to  colorless.  Rapidly  darkens  to  violet-brown  on 
exposure  to  light. 

Tests.  Very  easily  fusible  at  1.  B.  B.  on  charcoal  gives  a 
globule  of  silver.  Insoluble  in  nitric  acid,  but  slowly  soluble 
in  ammonium  hydroxide.  When  heated  with  galena  in  C.  T. 
gives  a  white  sublimate  of  lead  chloride.  Distinguished  chiefly 
by  its  horny  or  waxlike  appearance  and  its  sectility. 

Occurrence.  Cerargyrite  is  an  important  secondary  ore  of  silver. 
It  is  only  to  be  found  in  the  upper,  enriched  zone  of  silver  veins  where 
descending  waters  containing  small  amounts  of  chlorine  have  acted 
upon  the  oxidized  products  of  the  primary  silver  ores  of  the  vein. 
Found  associated  with  other  silver  ores,  galena,  etc.;  with  native  sil- 
ver, cerussite  and  secondary  minerals  in  general.  Was  an  important 
mineral  in  the  mines  at  Leadville  and  elsewhere  in  Colorado,  at  the 
Comstock  Lode  in  Nevada,  in  crystals  at  the  Poorman's  Lode  in 
Idaho.  Notable  amounts  have  been  found  in  Peru,  Chile  and 
Mexico,  and  in  the  silver  mines  of  Saxony. 

Name.  Cerargyrite  is  derived  from  two  Greek  words  mean- 
ing horn  and  silver,  in  allusion  to  its  hornlike  appearance  and 
characteristics. 

Use.    Silver  ore. 


Embolite. 

Composition,  Ag(Cl,Br).  Crystallization,  structure  and  physical 
properties,  like  those  of  Cerargyrite  (which  see).  Tests,  same  as  for 
cerargyrite,  except  that,  when  heated  in  C.  T.  with  galena,  it  gives 
a  lead  bromide  sublimate,  which  is  yellow  when  hot  and  white  when 
cold.  Occurrence,  same  as  for  cerargyrite,  with  which  it  is  usually 
found,  but  much  rarer. 


170 


MANUAL  OF  MINERALOGY 


Other  similar  silver -compounds  which  are  still  rarer  in  their 
occurrence  are,  bromyrite,  AgBr;  iodobromite,  Ag(Cl,Br,I);  My- 
rite,  Agl. 


Fluorite.     Fluor  Spar. 

Composition.      Calcium  fluoride,  CaF2  =  Fluorine  48.9,  cal- 
cium 51.1. 

Crystallization.  Isometric.  Habit  cubic  (Fig.  240)  often  in 
twinned  cubes  (Figs.  "241  and  242).  Other  forms  are  rare,  but 
examples  of  all  the  forms  of  the  Normal 
Class  have  been  observed;  the  tetrahexa- 
hedron  (Fig.  243)  and  hexoctahedron  (Fig. 
244)  are  characteristic. 

Structure.      Usually  crystallized.     Also 
massive;  coarse  or  fine  granular,  columnar. 
Physical  Properties.     Perfect  octahedral 
cleavage.     H.  =  4.     G.  =  3.18.    Transpar- 
Vitreous  luster.     Color  widely  various; 


Fig.  240. 

ent  to  sub  translucent. 

most  commonly  light  green,  yellow,  bluish  green  or  purple,  also 


Fig.  241. 


Fig.  242. 


colorless,  white,  rose,  blue,  brown.  A  single  crystal  may  show 
varying  bands  of  color;  the  massive  variety  is  also  often  banded 
in  color.  The  bluish  green  varieties  often  show  fluorescence 
(green  by  transmitted  light,  blue  by  reflected  light).  Some 
varieties  phosphoresce  when  heated,  giving  off  variously  colored 


FLUORITE 


171 


lights  which  are  independent  of  the  actual  color  of  the  specimen. 
The  variety  affording  a  green  light  is  known  as  chlorophane. 

Tests.  Fusible  at  3,  and  residue  gives  alkaline  reaction  to 
moistened  test  paper.  Gives  a  reddish  flame  (calcium).  When 
mixed  with  potassium  bisulphate  and  heated  in  C.  T.,  hydro- 


Fig.  243. 


Fig.  244. 


fluoric  acid  is  evolved  which  etches  the  glass,  and  a  white  deposit 
of  silica  forms  upon  the  walls  of  the  tube.  Determined  usually 
by  its  cubic  crystals  and  octahedral  cleavage,  also  vitreous  luster 
and  usually  fine  coloring,  and  by  the  fact  that  it  can  be  scratched 
with  a  knife. 

Occurrence.  A  common  and  widely  distributed  mineral.  Usually 
found  either  in  veins  in  which  it  is  the  chief  mineral  or  as  a  gangue 
mineral  with  metallic  ores,  especially  those  of  lead  and  tin.  Com- 
mon in  dolomites  and  limestone  and  has  been  observed  also  as  a 
minor  accessory  mineral  in  various  igneous  rocks.  Associated  with 
many  different  minerals,  as  calcite,  dolomite,  gypsum,  celestite, 
barite,  quartz,  galena,  sphalerite,  cassiterite,  topaz,  tourmaline, 
apatite. 

The  more  important  deposits  in  the  United  States  are  in  southern 
Illinois  near  Rosiclare,  and  in  the  adjacent  part  of  Kentucky.  The 
fluorite  occurs  here  in  limestone,  in  fissure  veins  which  at  times 
become  40  feet  in  width.  Fluorite  is  found  in  quantity  in  England, 
chiefly  from  Cumberland,  Derbyshire  and  Durham;  the  first  two 
localities  being  famous  for  their  magnificent  crystallized  specimens. 
Found  commonly  in  the  mines  of  Saxony. 

Use.  Fluorite  is  used  mainly  as  a  flux  in  the  making  of  steel, 
in  the  manufacture  of  opalescent  glass,  in  enameling  cooking 
utensils,  for  the  preparation  of  hydrofluoric  acid,  and  occasionally 
as  an  ornamental  material  in  the  form  of  vases,  dishes,  etc. 


172  MANUAL  OF  MINERALOGY 

Cryolite. 

Composition.  A  fluoride  of  sodium  and  aluminium,  NasAlF6 
=  Fluorine  54.4,  aluminium  12.8,  sodium  32.8. 

Crystallization.  Monoclinic.  Prominent  forms  are  prism 
and  base.  Crystals  rare,  usually  cubic  in  aspect,  and  in  parallel 
groupings  growing  out  of  massive  material. 

Structure.     Usually  massive. 

Physical  Properties.  H.=  2.5.  G.=  2.95-3.  Vitreous  to 
greasy  luster.  Colorless  to  snow-white.  Transparent  to  trans- 
lucent. A  low  index  of  refraction,  giving  the  mineral  an  appear- 
ance of  watery  snow  or  of  paraffin.  Powdered  mineral  almost 
disappears  when  immersed  in  water. 

Tests.  Easily  fusible  (1.5),  with  strong  yellow  sodium  flame. 
After  intense  ignition,  residue  gives  alkaline  reaction  on  moist- 
ened test  paper.  Fused  in  C.  T.  with  potassium  bisulphate, 
evolves  hydrofluoric  acid  and  gives  a  volatile  white  ring  of 
silica.  Characterized  by  its  massive  structure,  white  color  and 
peculiar  luster. 

Occurrence.  Occurs  in  a  large  vein  lying  in  granite  at  Arksuk- 
fiord  on  the  west  coast  of  Greenland.  The  following  minerals  are 
found  in  small  amounts  associated  with  the  cryolite:  quartz,  siderite, 
galena,  sphalerite,  pyrite,  chalcopyrite,  wolframite,  fluorite,  cassit- 
erite,  molybdenite,  arsenopyrite,  columbite.  Found  also  in  very 
small  amounts  at  Miask,  Ilmen  Mountains,  Siberia,  and  at  foot  of 
Pike's  Peak,  Colorado. 

Name.  Name  is  derived  from  two  Greek  words  meaning  frost 
and  stone,  in  allusion  to  its  icy  appearance. 

Use.  It  is  used  for  the  manufacture  of  sodium  salts,  of  certain 
kinds  of  glass  and  porcelain,  and  as  a  flux  in  the  electrolytic 
process  for  the  production  of  aluminium. 

2.   OXYCHLORIDES,   ETC. 

Atacamite. 

Composition.  Copper  chloride  with  copper  hydroxide, 
CuCl2.3Cu(OH)2  =  Chlorine  16.6,  copper  14.9,  cupric  oxide  55.81. 
water  12.7. 


CARNALLITE  173 

Crystallization.  Orthorhombic.  Commonly  slender  pris- 
matic in  habit,  with  vertical  striations.  Also  tabular  parallel 
to  brachypinacoid. 

Structure.  In  confused  crystalline  aggregates;  fibrous;  gran- 
ular. As  sand. 

Physical  Properties.  Cleavage  perfect  parallel  to  brachy- 
pinacoid. H.=  3-3.5.  G.  =  3.75-3.77.  Adamantine  to  vitre- 
ous luster.  Color  various  shades  of  green.  Transparent  to 
translucent. 

Tests.  Fusible  (3-4),  giving  an  azure-blue  flame  of  copper 
chloride.  B.  B.  on  charcoal  with  sodium  carbonate  gives  globule 
of  copper.  Nitric  acid  solution  with  silver  nitrate  gives  white 
precipitate  of  silver  chloride ;  with  ammonia  in  excess  gives  blue 
solution.  Gives  acid  water  in  C.  T.  Characterized  by  its 
green  color  and  granular  crystalline  structure.  Distinguished 
from  malachite  by  its  lack  of  effervescence  in  acids. 

Occurrence.  A  comparatively  rare  copper  mineral.  Found 
originally  as  sand  in  the  province  of  Atacama  in  Chile.  Occurs  with 
other  copper  ores  in  various  localities  in  Chile  and  Bolivia.  Found 
in  some  of  the  copper  districts  of  Australia;  occurs  sparingly  in  the 
copper  districts  of  Arizona. 

Use.    A  minor  ore  of  copper. 


3.   HYDROUS  CHLORIDES,  ETC 
Carnallite. 

A  hydrous  chloride  of  potassium  and  magnesium,  KCl.MgCl2. 
6HaO.  Orthorhombic.  Massive,  granular.  Crystals  rare.  Lus- 
ter nonmetallic,  shining,  greasy.  Color  milk-white,  often  reddish, 
due  to  included  hematite.  Transparent  to  translucent.  H.  =  1. 
G.=  1.6.  Bitter  taste.  Deliquescent.  Fusible  at  1-1.5  with  vio- 
let flame.  After  ignition  gives  an  alkaline  reaction  on  moistened 
test  paper.  Easily  and  completely  soluble  in  water;  on  addition  of 
nitric  acid  and  silver  nitrate  gives  a  white  precipitate  of  silver 
chloride.  Acid  solution  neutralized  with  ammonia  and  sodium 
phosphate  added  gives  a  white  precipitate  of  ammonium  magnesium 
phosphate.  Found  associated  with  halite,  sylvite,  etc.,  in  the  salt 
deposits  at  Stassfurt,  Prussia.  Used  as  a  source  of  potassium 
compounds. 


174 


MANUAL  OF  MINERALOGY 


OXIDES. 

The  oxides  are  subdivided  into  three  sections:  (1)  Oxides  of 
Silicon;  (2)  Oxides  of  the  Semimetals;  (3)  Oxides  of  the  Metals. 

1.   OXIDES  OF  SILICON. 

Quartz. 

Composition.  Silicon  dioxide,  Si02  =  Oxygen  53.3,  silicon 
46.7.  Often  with  various  impurities. 

Crystallization.  Hexagonal-rhombohedral;  trapezohedral. 
Crystals  commonly  prismatic,  with  prism  faces  horizontally 
striated.  Terminated  usually  by  a  combination  of  a  positive 
and  negative  rhombohedron,  which  often  are  so  equally  devel- 
oped as  to  give  the  effect  of  a  hexagonal  pyramid  (Fig.  245). 


Fig.  245. 


Fig.  246. 


Fig.  247. 


Sometimes  one  rhombohedron  predominates  or  occurs  alone 
(Fig.  246) .  At  times  the  prism  faces  are  wanting,  and  the  com- 
bination of  the  two  rhombohedrons  gives  what  appears  to  be  a 
doubly  terminated  hexagonal  pyramid  (known  as  a  quartzoid) 
(Fig.  247).  Crystals  at  times  very  much  distorted,  when  the 
recognition  of  the  prism  faces  by  their  horizontal  striations  will 
assist  in  the  orientation  of  the  crystal.  The  trapezohedral  faces 
are  to  be  occasionally  observed  as  small  truncations  between  a 
prism  face  and  that  of  an  adjoining  rhombohedron  either  to  the 
right  or  left,  forming  what  are  known  as  right-  or  left-handed 
crystals  (Figs.  248  and  249).  Crystals  are  often  elongated  in 
tapering  and  sharply  pointed  forms,  due  to  an  oscillatory  com- 
bination between  the  faces  of  the  different  rhombohedrons  and 


QUARTZ 


175 


those  of  the  prism  (A,  PI.  VI).     Sometimes  twisted  and  bent. 
Crystals  frequently  twinned.    The  twins  at  times  are  so  inti- 


Fig.  248.     Right-handed  Crystal. 


Fig.  249.    Left-handed  Crystal. 


mately  intergrown  that  they  can  only  be  determined  by  the 
irregular  position  of  the  trapezohedral  faces,  by  etching  the 
crystal  or  by  the  pyroelectric  phenomena  that  they  show. 

Structure.  Commonly  in  crystals.  From  large  crystals 
usually  attached  at  one  end,  to  finely  crystalline  coatings,  form- 
ing "drusy"  surfaces.  Also  common  in  massive  forms  of  great 
variety.  From  coarse-  to  fine-grained  crystalline  to  flintlike  or 
cryptocrystalline  varieties.  Sometimes  in  concretionary  forms, 
mammillary,  etc.  As  sand. 

Physical  Properties.  H.=  7.  G.  =  2.65-2.66.  Vitreous  lus- 
ter, sometimes  greasy,  splendent  to  nearly  dull.  Color  widely 
various.  Usually  colorless  or  white,  but  frequently  colored  by 
various  impurities,  yellow,  red,  pink,  amethyst,  green,  blue, 
brown,  black.  Transparent  to  opaque.  Conchoidal  fracture. 

Tests.  Infusible.  Insoluble.  Yields  a  clear  glass  when  the 
finely  powdered  mineral  is  fused  with  an  equal  volume  of  sodium 
carbonate.  Usually  told  by  its  glassy  luster,  conchoidal  fracture, 
hardness  (7)  and  crystal  form. 

Varieties.  A  great  many  different  forms  of  quartz  exist  to 
which  varietal  names  have  been  given.  The  more  important 
varieties  with  a  brief  description  of  each  follow. 

A.   CRYSTALLINE   VARIETIES. 


1.   Rock   Crystal. 
crystals. 


Colorless  quartz,   commonly   in  distinct 


176  MANUAL  OF  MINERALOGY 

2.  Amethyst.    Quartz  colored  purple  or  violet,  often  crys- 
tallized. 

3.  Rose  Quartz.    Usually  massive,  color  a  rose-red  or  pink. 
Often  fades  somewhat  on  exposure  to  light. 

4.  Smoky  Quartz;  Cairngorm  Stone.     Crystallized  quartz  of  a 
smoky  yellow  to  brown  and  almost  black  color.     Named  cairn- 
gorm from  the  locality  of  Cairngorm  in  Scotland. 

5.  Milky  Quartz.     Milky  white  in  color  and  nearly  opaque. 
Sometimes  with  greasy  luster. 

6.  Cat's-eye.    A  stone,  which  when  cut  in  a  round  shape  (en 
cabochon)  exhibits  an  opalescent  or  chatoyant  effect,  as  it  is 
termed,  is  called  a  cat's-eye.    Quartz  among  other  minerals  gives 
at  times  this  effect,  which  is  due  either  to  fibrous  inclusions  or 
to  a  fibrous  structure  of  the  quartz  itself.     The  latter  is  seen  in 
the  tiger's-eye,  a  yellow  fibrous  quartz  from  South  Africa,  which 
is  pseudomorphic  after  another  fibrous  mineral,  crocidolite. 

7.  With  Inclusions.     Many  other  minerals  occur  at  times  as 
inclusions  in  quartz.     Rutilated  quartz  has  fine  needles  of  rutile 
penetrating  it.     Tourmaline  and  other  minerals  are  found  in 
quartz  in  the  same  way.     Aventurine  is  quartz  including  brilliant 
scales  of  hematite  or  mica.     Liquids  and  gases  at  times  occur 
as  inclusions;   both  liquid  and  gaseous  carbon  dioxide  exist  in 
some  quartz. 

B.    CRYPTOCRYSTALL1NE  VARIETIES. 

1.  Chalcedony.    An  amorphous  quartz  material,  translucent 
with  a  waxy  luster.    White,  yellowish  brown  to  dark-brown  in 
color.    Often  mammillary,  stalactitic,  etc.,  in  structure.     De- 
posited from  aqueous  solutions  and  found  lining  or  filling  cavities 
in  rocks  (see  Fig.  B,  pi.  III). 

2.  Cornelian.    A  red  chalcedony. 

3.  Chrysoprase.    An  apple-green  chalcedony. 

4.  Agate.    A  variegated  chalcedony.    The  different   colors 
usually  in  delicate,  fine  parallel  bands  which  are  commonly 
curved,  sometimes  concentric  (Fig.  B,  pi.  VI).     The  color  is 
sometimes  strengthened  or  even  changed  by  artificial  means. 
Some  agates  have  the  different  colors  arranged  not  in  bands  but 


PLATE  VI. 


A.    Smoky  Quartz,  Pike's  Peak,  Colorado. 


B.    Agate,  Oberstein,  Germany. 


QUARTZ  177 

irregularly  distributed.  Moss  agate  is  a  variety  in  which  the 
variation  in  color  is  due  to  visible  impurities,  often  manganese 
oxide. 

5.  Onyx.    A  banded  chalcedony  like  agate,  except  the  bands 
are  arranged  in  straight  parallel  lines. 

6.  Flint.    Something  like  chalcedony  but  of  dull,  often  dark 
color.     It  breaks  with  a  prominent  conchoidal  fracture  and  gives 
a  sharp  edge.     Used  for  various  implements  by  early  man. 

7.  Jasper.     Opaque  quartz,  usually  colored  red  from  hematite 
inclusions. 

Occurrence.  Quartz  is  the  most  common  of  minerals.  Occurs 
as  an  important  constituent  of  the  acid  igneous  rocks,  such  as 
granite,  rhyolite,  pegmatite,  etc.  It  is  a  common  mineral  of  sedi- 
mentary rocks,  forming  the  chief  mineral  in  sandstone.  Occurs 
largely  also  in  metamorphic  rocks,  as  gneisses  and  schists,  while  it 
forms  practically  the  only  mineral  of  quartzites.  Deposited  often 
from  solution  and  forms  the  most  common  vein  and  gangue  mineral. 
In  rocks  it  is  associated  chiefly  with  feldspar  and  muscovite;  in 
veins  with  practically  the  entire  range  of  vein  minerals.  Often 
carries  gold  and  becomes  an  important  ore  of  that  metal.  Occurs 
in  large  amount  as  sand  in  stream  beds  and  upon  the  seashore  and 
as  a  constituent  of  soils. 

Rock  crystal  is  found  widely  distributed,  some  of  the  more  notable 
localities  being:  the  Alps;  Minas  Geraes  and  Goyoz,  Brazil;  on  the 
island  of  Madagascar;  in  Japan.  The  best  quartz  crystals  from  the 
United  States  are  found  at  Hot  Springs,  Arkansas,  and  Little  Falls, 
New  York.  Important  occurrences  of  amethyst  are  located  in  the 
Ural  Mountains  and  in  Brazil.  Found  at  Thunder  Bay  on  the  north 
shore  of  Lake  Superior  and  in  the  United  States  in  Oxford 
County,  Maine;  Delaware  and  Chester  counties,  Pennsylvania; 
Black  Hills,  South  Dakota,  etc.  Smoky  quartz  is  found  in  large  and 
fine  crystals  in  Canton  Uri,  Switzerland;  at  Pike's  Peak,  Colorado; 
Alexander  County,  North  Carolina;  at  Auburn,  Maine,  etc.  The 
chief  source  of  agates  at  present  is  a  district  in  southern  Brazil  and 
northern  Uruguay.  They  are  mostly  cut  at  Oberstein,  Germany, 
itself  a  famous  agate  locality.  Found  in  Laramie  County,  Wyoming, 
and  numerous  other  places  in  the  United  States.  Massive  quartz, 
occurring  in  quartz  veins  or  with  feldspar  in  pegmatite  veins,  is 
mined  for  its  various  commercial  uses  in  Connecticut,  New  York, 
Maryland,  Wisconsin,  etc. 

Use.  Widely  used  in  its  various  colored  forms  as  ornamental 
material,  as  amethyst,  rose  quartz,  cairngorm,  cat's-eye,  tiger's- 


178  MANUAL  OF  MINERALOGY 

eye,  aventurine,  carnelian,  agate,  onyx,  etc.  Used  for  abrading 
purposes  either  as  quartz  sand  or  as  sandpaper.  Used  in  the 
manufacture  of  porcelain,  of  glass,  as  a  wood  filler,  in  paints, 
scouring  soaps,  etc.  As  sand  is  used  in  mortars  and  cements. 
As  quartzite,  sandstone,  and  in  its  various  other  rock  forms  as 
a  building  stone,  for  paving  purposes,  etc.  Large  amounts  of 
quartz  sand  are  used  as  an  acid  flux  in  certain  smelting  opera- 
tions. 

Opal. 

Composition.  Silicon  dioxide,  like  quartz,  with  a  varying 
amount  of  water,  Si02nH20. 

Crystallization.     Amorphous. 

Structure.     Massive;   often  botryoidal,  stalactitic,  etc. 

Physical  Properties.  H.  =  5.5-6.5.  G.  =  1.9-2.3.  Vitre- 
ous luster;  often  somewhat  resinous.  Colorless,  white,  pale 
shades  of  yellow,  red,  brown,  green,  gray  and  blue.  With 
darker  colors,  which  are  due  to  various  impurities.  .  Often  has 
a  milky  or  "opalescent"  effect  and  sometimes  shows  a  fine  play 
of  colors.  Transparent  to  opaque. 

Tests.  Infusible.  Insoluble.  Reacts  like  quartz.  Gives  a 
little  water  upon  intense  ignition  in  C.  T. 

Varieties.  Precious  Opal.  White,  milky  blue,  yellow.  Some- 
times dark,  as  in  so-called  black  opal.  Translucent,  with  an 
internal  play  of  colors.  This  phenomenon  is  said  to  be  due  to 
thin  curved  laminae  which  refract  the  light  differently  from  the 
mass  of  the  material,  and  so  serve  to  break  it  up  into  the  various 
prismatic  colors.  Fire  opal  is  a  variety  with  intense  orange  to 
red  reflections. 

Common  Opal.  Milk-white,  yellow,  green,  red,  etc.,  without 
internal  reflections. 

Hyalite.  Clear  and  colorless  opal  with  a  globular  or  botry- 
oidal structure. 

Geyserite.  Opal  deposited  by  hot  springs  and  geysers.  Found 
about  the  geysers  in  the  Yellowstone  Park. 

Wood  Opal.     Fossil  wood  with  opal  as  the  petrifying  material. 

Tripolite,  or  Infusorial  earth.     Fine-grained  deposits,  resem- 


CUPRITE  179 

bling  chalk  in  appearance.     Formed  by  the  accumulation  of  the 
siliceous  shells  of  small  sea  organisms. 

Occurrence.  Opal  is  found  lining  and  filling  cavities  in  igneous 
and  sedimentary  rocks,  where  it  has  evidently  been  deposited  through 
the  agency  of  hot  waters.  In  its  ordinary  variety  it  is  of  widespread 
occurrence.  Precious  opals  are  found  at  Czernowitza,  Hungary; 
in  Queretaro  and  other  states  in  Mexico;  in  Honduras;  and  from 
various  localities  in  Australia,  the  chief  district  being  White  Cliffs, 
New  South  Wales.  Recently  black  opal  has  been  found  in  Idaho. 

Use.  As  a  gem.  The  stones  are  usually  cut  in  round  shapes, 
en  cabochon,  and  gems  of  one-carat  size  are  valued  up  to  $20. 
Stones  of  large  size  and  exceptional  quality  are  very  highly 
prized. 

2.   OXIDES   OF  THE  SEMIMETALS. 
The  minerals  of  this  division  are  all  rare  in  occurrence.    Some 
of  the  more  important  species  are,  arsenolite,  As203;  senarmon- 
tite,  Sb203;  valentinite,  Sb203;  tellurite,  Te02;  tungstite,  W03;  cer~ 
vantite,  Sb204. 

3.   OXIDES  OF  THE  METALS. 

The  oxides  of  the  metals  are  grouped  into  two  main  divisions: 
A.  Anhydrous  Oxides;  B.  Hydrous  Oxides.  Further,  the  Anhy- 
drous Oxides  are  further  subdivided  into:  (1)  Protoxides;  (2) 
Sesquioxides;  (3)  Intermediate  Oxides;  (4)  Dioxides. 

A.   ANHYDROUS   OXIDES. 
1.   PROTOXIDES. 

Cuprite.     Ruby  Copper.     Red  Copper  Ore. 

Composition.  Cuprous  oxide,  Cu20  =  Oxygen  11.2,  copper 
88.8. 

Crystallization.  Isometric.  Common 
forms  are  cube,  octahedron  and  dodecahedron, 
frequently  in  combination  (Fig.  250).  Some- 
times in  much  elongated  cubic  crystals,  ca- 
pillary in  size;  known  as  "plush  copper"  or 
chalcotrichite.  Fig.  250. 


180  MANUAL  OF  MINERALOGY 

Structure.  Usually  massive,  more  rarely  in  crystals  or  capil- 
lary forms. 

Physical  Properties.  H.  =  3.5-4.  G.  =  6.  Luster  adaman- 
tine in  clear  crystallized  varieties  to  submetallic  and  earthy  in 
massive  varieties.  Color  red  of  various  shades.  Ruby-red  in 
transparent  crystals.  Streak  brownish  red,  Indian-red.  High 
index  of  refraction,  giving  brilliant  luster  to  transparent  variety. 

Tests.  Easily  fusible  at  3,  giving  emerald-green  flame,  or, 
if  moistened  with  hydrochloric  acid  and  then  heated,  flame  is 
azure-blue.  Gives  globule  of  copper  on  charcoal  in  R.  F. 
When  dissolved  in  small  amount  of  concentrated  hydrochloric 
acid  and  solution  diluted  with  cold  water  gives  a  white  precipi- 
tate of  cuprous  chloride  (test  for  cuprous  copper).  Usually  to 
be  determined  by  its  color  and  streak. 

Occurrence.  An  important  ore  of  copper  of  secondary  origin. 
Found  in  the  upper,  oxidized  portions  of  copper  veins,  associated 
with  the  other  secondary  copper  minerals,  native  copper,  malachite, 
azurite,  chrysocolla,  etc.  Found  in  the  United  States  in  connection 
with  the  copper  deposits  at  Bisbee,  Morenci,  etc.,  Arizona.  Found  in 
small  amount  with  the  native  copper  from  Lake  Superior.  An  im- 
portant ore  in  Chile,  Peru  and  Bolivia.  Fine  crystals  come  from 
Bisbee,  Arizona;  Cornwall,  England;  Chessy,  France;  the  Urals. 

Name.     Derived  from  the  Latin,  cuprum,  copper. 
Use.     Ore  of  copper. 

Zincite. 

Composition.  Zinc  oxide,  ZnO  =  Oxygen  19.7,  zinc  80.3. 
Manganese  protoxide  often  present. 

Crystallization.  Hexagonal;  hemimorphic.  Terminated 
above  by  faces  of  a  steep  pyramid  and  below  with  a  basal 
plane.  Sometimes  shows  short  prism. 

Structure.     Usually  massive  with  platy  or  granular  structure. 

Physical  Properties.  Perfect  basal  cleavage.  H.  =  4-4.5. 
G.  =  5.5.  Luster  subadamantine.  Color  deep  red  to  orange- 
yellow.  Streak  orange-yellow.  Translucent  to  almost  opaque. 

Tests.  Infusible.  Soluble  in  hydrochloric  acid.  When  the 
finely  powdered  mineral  is  mixed  with  sodium  carbonate  and 
charcoal  dust  and  intensely  heated  B.  B.,  gives  a  nonvolatile 


CORUNDUM 


181 


coating  of  zinc  oxide,  yellow  when  hot,  white  when  cold.  Usually 
with  borax  bead  in  0.  F.  gives  a  reddish  violet  color  (manganese). 
Told  chiefly  by  its  color  and  streak. 

Occurrence.  Found  in  the  zinc  deposits  at  Franklin  Furnace, 
New  Jersey,  associated  with  franklinite  and  willemite,  often  in  an 
intimate  mixture.  Sometimes  embedded  in  pink  calcite. 

Use.  An  ore  of  zinc,  particularly  used  for  the  production  of 
zinc  white  (zinc  oxide). 

In  this  division  also  belong  water,  ice,  H20,  which  is  hexagonal 
in  crystallization,  and  tenorite  or  melaconite,  CuO. 

2.    SESQUIOXIDES. 
HEMATITE   GROUP. 

The  Hematite  Group  includes  the  closely  related  rhombohe- 
dral  minerals,  corundum,  A1203,  hematite,  Fe203,  and  ilmenite 
(Fe,Ti)203. 

Corundum. 

Composition.  Aluminium  oxide,  A1203  =  Oxygen  47.1,  alu- 
minium 52.9. 

Crystallization.  Hexagonal-rhombohedral.  Crystals  usually 
prismatic  in  habit  or  tapering  hexagonal  pyramids  (Figs.  251  and 


Fig.  251.  Fig.  252.  Fig.  253. 

252).  Often  rounded  into  barrel  shapes  (Fig.  253).  Frequently 
with  deep  horizontal  striations.  At  times  shows  rhombohedral 
and  pyramidal  faces. 


182  MANUAL  OF  MINERALOGY 

Structure.  Rudely  crystallized  or  massive  with  parting  planes 
nearly  cubic  in  angle;  coarse  or  fine  granular. 

Physical  Properties.  Parting  basal  and  rhombohedral,  the 
latter  giving  nearly  cubic  blocks.  H.  =  9  (next  to  the  diamond 
in  hardness).  G.  =  3.95-4.1  (unusually  high  for  a  nonmetallic 
mineral).  Adamantine  to  vitreous  luster.  Color  various.  Usu- 
ally some  shade  of  brown,  pink  or  blue.  May  be  white,  gray, 
green,  ruby-red  or  sapphire-blue.  Transparent  to  opaque. 

Tests.  Infusible.  Insoluble.  Finely  pulverized  material 
moistened  with  cobalt  nitrate  and  intensely  ignited  assumes  a 
blue  color  (aluminium).  Characterized  chiefly  by  its  great 
hardness,  adamantine  luster  and  high  specific  gravity. 

Varieties.  Ordinary  Corundum.  In  translucent  to  opaque 
masses,  showing  often  the  nearly  cubical  parting;  also  granular 
to  compact. 

Gem  Corundum.  When  transparent  and  finely  colored,  corun- 
dum furnishes  various  gem  stones.  The  ruby  is  deep  red  corun- 
dum; sapphire  is  blue  corundum.  Stones  of  other  colors  are 
sometimes  spoken  of  as  yellow,  violet,  etc.,  sapphires  or  are 
designated  by  prefixing  the  word  oriental  to  the  name  of  some 
other  mineral  similar  in  color;  thus,  oriental  topaz  is  a  brownish 
yellow  corundum;  oriental  amethyst,  a  reddish  violet  corundum, 
etc. 

Emery.  Is  a  fine-grained  corundum  mixed  with  other  min- 
erals, chiefly  magnetite. 

Occurrence.  Common  in  the  metamorphic  rocks,  such  as  crys- 
talline limestone,  mica-schist,  gneiss,  etc.  Found  also  as  an  original 
constituent  of  certain  igneous  rocks,  usually  those  deficient  in  silica. 
Found  sometimes  in  large  masses,  evidently  the  product  of  magmatic 
differentiation.  Found  frequently  in  crystals  and  rolled  pebbles  in 
detrital  soil  and  stream  sands,  where  it  has  been  preserved  through 
its  hardness.  Associated  minerals  are  commonly  chlorite  micas, 
chrysolite,  serpentine,  magnetite,  spinel,  cyanite,  diaspore,  etc. 

Rubies  are  found  chiefly  in  Burmah,  Siam  and  Ceylon.  The 
most  important  locality  in  Burmah  is  near  Mogok,  90  miles  north 
of  Mandalay.  The  stones  are  found  here  chiefly  in  the  soil  resulting 
from  the  decay  of  a  metamorphosed  limestone.  They  have  also 
been  found  in  situ  in  the  limestone.  The  rubies  of  Siam  are  found 
near  Bangkok,  on  the  Gulf  of  Siam,  where  they  occur  in  a  clay, 


CORUNDUM  183 

derived  from  the  decomposition  of  a  basalt.  The  rubies  of  Ceylon 
are  found  with  other  gem  stones  in  the  stream  gravels.  A  few 
rubies  have  been  found  in  the  gravels  and  in  connection  with  the 
larger  corundum  deposits  of  North  Carolina. 

Sapphires  are  found  associated  with  the  rubies  of  Siam  and  Cey- 
lon. They  occur  also  at  Banskar  in  Cashmere,  India.  In  the 
United  States  small  sapphires  of  fine  color  are  found  in  various -lo- 
calities in  Montana.  They  were  first  found  in  the  river  sands  east 
of  Helena  when  washing  them  for  gold.  They  have  since  been 
found  embedded  in  the  rock  of  lamprophyre  dikes.  The  rock  is 
quarried  and  after  exposure  to  the  air  for  a  time  it  gradually  de- 
composes, setting  the  sapphires  free.  Sapphires  are  also  found 
over  an  extensive  area  in  central  Queensland,  Australia. 

Massive  corundum  is  found  in  the  United  States  in  various  locali- 
ties along  the  eastern  edge  of  the  Appalachian  Mountains  from  North 
Carolina  south.  It  has  been  extensively  mined  in  southwestern 
North  Carolina.  It  occurs  here  in  large  masses  lying  at  the  edges 
of  intruded  masses  of  a  chrysolite  rock  (dunite)  and  is  thought  to 
have  been  a  separation  from  the  original  magma.  Found  as  an 
original  constituent  of  a  nepheline  syenite  in  the  Province  of  Ontario, 
Canada.  At  times  the  corundum  is  so  abundant  as  to  form  more 
than  10  per  cent  of  the  rock  mass. 

The  impure  corundum,  known  as  emery,  is  found  in  large  quanti- 
ties on  Cape  Emeri  on  the  island  of  Naxos  and  in  various  localities 
in  Asia  Minor.  In  the  United  States  emery  has  been  extensively 
mined  at  Chester,  Massachusetts. 

Artificial.  Artificial  corundum  is  now  being  made  in  the  elec- 
trical furnaces  at  Niagara.  Small  synthetic  rubies  and  sapphires, 
colored  with  minute  amounts  of  chromium,  have  been  success- 
fully made.  Also  small  grains  of  the  natural  stone  have  been 
fused  together  into  larger  masses,  from  which  stones  of  two  or 
three  carats  in  size  can  be  cut.  These  are  known  as  recon- 
structed rubies  arid  sapphires. 

Use.  As  a  gem  stone.  The  ruby  at  times  yields  the  most 
valuable  of  gems;  a  stone  of  the  deep  red  known  as  "pigeon's 
blood"  may  bring  $1500  to  $2000  a  carat.  The  blue  sapphire  is 
less  valuable,  ranging  at  times,  however,  as  high  as  $125  a  carat. 
Corundum  stones  of  various  other  color  are  valued  up  to  $30 
a  carat. 

Used  also  as  an  abrasive,  either  ground  from  the  pure  massive 
material,  or  in  its  impure  form  as  emery.  Artificial  corundum 


184 


MANUAL  OF  MINERALOGY 


and  carborundum,  which  in  composition  is  a  carbide  of  silicon, 
are  now  manufactured  on  a  large  scale  in  electric  furnaces  and 
are  being  used  in  considerable  amount  as  abrasives  instead  of 
the  naturally  occurring  corundum. 

Hematite. 

Composition.  Iron  sesquioxide,  Fe203  =  Oxygen  30,  iron  70. 
Sometimes  with  titanium  and  magnesium,  passing  into  ilmenite. 

Crystallization.  Hexagonal-rhombohedral.  Crystals  usually 
thick  to  thin  tabular.  Basal  planes  prominent,  often  showing 


Fig.  254. 


Fig.  255. 


triangular  markings  (Figs.  254  and  255).     Edges  of  plates  some- 
times beveled  with  rhombohedral  and  pyramidal  forms  (Fig. 


Fig.  256. 


Fig.  257. 


256).  Thin  plates  at  times  grouped  in  rosette  forms  (iron  roses) 
(Fig.  257).  More  rarely  crystals  are  distinctly  rhombohedral, 
often  with  nearly  cubic  angles. 

Structure.  Usually  earthy  or  in  botryoidal  to  reniform  shapes 
with  radiating  structure.  At  times  micaceous;  crystallized. 

Physical  Properties.  Rhombohedral  parting  with  nearly  cubic 
angles.  H.  =  5.5-6.5.  G.  =  4.8-5.3.  Metallic  luster.  Color 
reddish  brown  to  black.  Streak  light  to  dark  Indian-red. 

Tests.  Infusible.  Becomes  strongly  magnetic  on  heating  in 
R.  F.  Slowly  soluble  in  hydrochloric  acid;  solution  with  potas- 
sium ferrocyanide  gives  dark  blue  precipitate  (test  for  ferric 
iron).  Told  chiefly  by  its  characteristic  Indian-red  streak. 


HEMATITE  185 

Varieties.  Specular  Hematite.  Black  hematite  with  brilliant 
splendent  luster  (whence  name,  specular,  mirrorlike),  in  crystals 
or  in  foliated  masses  with  micaceous  structure. 

Columnar  to  Reniform  Hematite,  Kidney  Ore.  Brownish  black 
color,  in  columnar  to  reniform  shapes  with  radiating  structure, 
having  fibrous  appearance  (A,  pi.  III). 

Oolitic  and  Fossil  Ore.  Impure  hematite  in  small  globular  or 
lenticular  concretions.  At  times  with  fossils. 

Earthy  Hematite.  In  pulverulent,  earthy  form  of  various 
shades  of  reddish  brown.  Often  somewhat  hydrated  and  pass- 
ing into  limonite. 

Occurrence.  Hematite  is  a  widely  distributed  mineral  in  rocks 
of  all  ages  and  forms  the  most  abundant  ore  of  iron.  Occurs  as  an 
accessory  mineral  in  feldspathic  igneous  rocks,  such  as  granite. 
Found  from  microscopic  scales  to  enormous  masses  in  connection 
with  metamorphic  rocks.  It  is  found  in  red  sandstones  as  the 
cementing  material  that  binds  the  quartz  grains  together. 

The  crystallized  variety  is  found  at  many  places,  more  particu- 
larly from  the  island  of  Elba;  St.  Gothard,  Switzerland,  in  "iron 
roses " ;  in  the  lavas  of  Vesuvius;  at  Cleator  Moor,  Cumberland,  etc. 
In  the  United  States  the  columnar  and  earthy  varieties  are  found 
in  enormous  beds  that  furnish  a  large  proportion  of  the  iron  ore  of 
the  world.  The  chief  iron-ore  districts  of  the  United  States  are 
grouped  around  the  southern  and  northwestern  shores  of  Lake 
Superior  in  Michigan,  Wisconsin  and  Minnesota.  The  chief  dis- 
tricts, which  are  spoken  of  as  iron-ore  ranges,  are,  from  east  to  west, 
the  Marquette  Range  in  northern  Michigan;  the  Menominee  Range 
in  Michigan  to  the  southwest  of  the  Marquette;  the  Penokee- 
Gogebic  Range  in  northern  Wisconsin;  the  Mesabi  Range,  north 
of  Duluth  in  Minnesota;  and  the  Vermillion  Range  farther  north 
in  Minnesota,  near  the  Canadian  boundary.  The  iron  ore  of  these 
different  ranges  varies  from  the  hard  black  micaceous  specular 
variety  to  the  soft  red  earthy  type.  All  of  the  ore  bodies  lie  in  rock 
troughs  which  furnish  impervious  underlying  basements  to  the 
deposits.  In  all  of  the  districts,  except  the  Mesabi,  these  under- 
lying rocks  are  in  the  nature  of  altered  igneous  dikes,  known  aa 
soapstone  dikes.  The  ore  bodies  lie  in  more  or  less  broken  quartz 
material,  frequently  colored  red  by  inclusions  of  hematite  and  called 
jasper.  The  origin  of  these  deposits  is  attributed  to  the  slow  con- 
centration of  the  iron  content  of  a  siliceous  carbonate  rock  by  down- 
ward moving  waters.  These  waters  were  at  last  collected  in  the 
impervious  rock  troughs  and  there  deposited  their  iron  content  by 


186  MANUAL  OF  MINERALOGY 

a  replacement  of  the  quartz  of  the  overlying  rock.  The  ores  are 
mined  in  part  by  underground  methods,  and  in  part,  where  the  ore  is 
soft  and  lies  sufficiently  near  the  surface,  by  the  use  of  steam  shovels. 
Hematite  is  also  found  in  the  United  States  in  various  places  in 
connection  with  the  outcrop  of  rocks  of  the  Clinton  formation,  from 
central  New  York  south  along  the  line  of  the  Appalachian  Moun- 
tains to  central  Alabama.  The  most  important  deposits  of  the 
series  lie  in  eastern  Tennessee  and  northern  Alabama,  near  Birming- 
ham. Hematite  has  been  found  at  Iron  Mountain  and  Pilot  Knob 
in  southeastern  Missouri.  Deposits  of  considerable  importance  are 
located  in  Wyoming,  in  Laramie  and  Carbon  counties. 

Name.  Derived  from  a  Greek  word  meaning  blood,  in  allusion 
to  the  color  of  the  powdered  mineral. 

Ilmenite.     Menaccanite.     Titanic  Iron  Ore. 

Composition.  Ferrous  titanate,  FeTi03  =  Oxygen  31.6,  tita- 
nium 31.6,  iron  36.8.  By  the  introduction  of  ferric  oxide,  the 
ratio  between  the  titanium  and  iron  often  varies  widely.  Some- 
times contains  magnesium  replacing  the  ferrous  iron. 

Crystallization.  Hexagonal-rhombohedral ;  tri-rhombohe- 
dral.  Crystals  usually  thick  tabular  with  prominent  basal  planes 
and  small  rhombohedral  truncations.  Faces  of  the  third  order 
rhombohedron  rare.  Crystal  angles,  etc.,  close  to  those  for 
hematite. 

Structure.  Usually  massive,  compact;  also  in  grains  or  as 
sand.  Often  in  thin  plates. 

Physical  (Properties.  H.  =  5.5-6.  G.=4.7.  Metallic  to 
submetallic  luster.  Color  iron-black.  Streak  black  to  brownish 
red.  Sometimes  magnetic  without  heating. 

Tests.  Infusible.  May  be  magnetic  without  heating.  Fine 
powder  fused  in  R.  F.  with  sodium  carbonate  yields  a  magnetic 
mass.  After  fusion  with  sodium  carbonate  the  fusion  can  be 
dissolved  in  hydrochloric  acid,  and  when  the  solution  is  boiled 
with  tin  it  assumes  a  violet  color  (titanium). 

Occurrence.  Occurs  as  beds  and  lenticular  bodies  enveloped  in 
gneiss  and  other  crystalline  metamorphic  rocks.  Often  associated 
with  magnetite.  Also  as  an  accessory  mineral  in  eruptive  rocks. 
Found  in  large  quantities  at  Kragero  and  other  localities  in  Norway; 


SPINEL  187 

at  Miask  in  the  Ilmen  Mountains;  at  Bay  St.  Paul  in  Quebec, 
Canada.  Found  at  Washington,  Connecticut;  in  Orange  County, 
New  York,  etc. 

Use.  Has  practically  no  commercial  use.  A  little  of  it  pres- 
ent in  a  body  of  magnetite  iron  ore  makes  the  ore  so  difficult  to 
smelt  as  to  render  it  of  little  value. 

3.    INTERMEDIATE    OXIDES. 
SPINEL   GROUP. 

A  group  of  oxides  which  in  composition  are  combinations  of  a 
bivalent  oxide  with  a  trivalent  oxide,  the  general  formula  being, 
R"O.R2'"03.  R"0  may  be  MgO,  ZnO,  FeO,  MnO,  while  R2///03 
may  be  A1203,  Fe203,  Mn203,  Cr203.  The  chief  members  of  the 
group  are  as  follows: 

Spinel,  Mg  O.A1203  or  MgAl204. 

Gahnite,  ZnO.Al203  or  ZnAl204. 

Magnetite,  FeO.Fe203  or  FeFe204. 

Franklinite,  (Fe,Mn,Zn)0.(Fe,Mn)203 
or  (Fe,Mn,Zn)(Fe,Mn)2O4. 

Chromite,  (Fe,Mg)O.Cr203  or  (Fe,Mg)Cr204. 

The  crystalline  habit  of  all  the  members  of  the  group  is  octa- 
hedral. The  dodecahedron  is  sometimes  present,  but  other  forms 
are  rare. 

Spinel. 

Composition.     MgAl204  or  MgO. A1203  =  Alumina  71.8,  mag- 
nesia 28.2.     The  magnesium  may  be, 
in  part,  replaced  by   ferrous  iron  or 
manganese   and    the    aluminium    by 
ferric  iron  and  chromium. 

Crystallization.  Isometric.  Habit 
strongly  octahedral  (Fig.  258).  Some- 
times in  twinned  octahedrons  (spinel 
twins)  (Fig.  259).  Dodecahedron  at 
times  as  small  truncations  (Fig.  260). 
Other  forms  rare.  Fig-  258' 


188  MANUAL  OF  MINERALOGY 

Structure.     Usually  crystallized. 

Physical  Properties.  H.=  8.  G.  =  3.5-4.1.  Nonmetallic. 
Vitreous  luster.  Color  various,  —  red,  lavender,  blue,  green, 
brown,  black,  sometimes  almost  white.  Streak  white.  Usually 
translucent  to  opaque,  at  times  clear  and  transparent. 


Fig.  259.  Fig.  260. 

Tests.  Infusible.  The  finely  powdered  mineral  dissolves 
completely  B.  B.  in  the  salt  of  phosphorus  bead  (proving  the 
absence  of  silica).  Recognized  chiefly  by  its  hardness  (8),  its 
octahedral  crystals  and  vitreous  luster. 

Varieties.  1.  Ruby  Spinel.  Nearly  pure  magnesian  spinel. 
Clear  red;  transparent  to  translucent.  When  rose-red  known 
as  balas  ruby,  yellow  or  orange-red,  rubicelle;  violet-red,  alman- 
dine  ruby. 

2.  Pkonaste.    Iron-magnesia  spinel.    Color  dark  green,  brown 
to  black.     Opaque  or  nearly  so. 

3.  Chlorospinel.    Magnesia-iron  spinel.    Color  grass-green  ow- 
ing to  the  presence  of  copper. 

4.  Picotite,  or  Chrome  Spinel.    Contains  chromium  and  has 
iron  replacing  magnesium.     Color  yellowish  or  greenish  brown. 
Translucent  to  opaque. 

Occurrence.  A  common  metamorphic  mineral  occurring  em- 
bedded in  granular  limestone,  associated  with  calcite,  serpentine, 
etc.  Occurs  also  as  an  accessory  mineral  in  many  basic  igneous 
rocks,  as  peridotites,  etc.  Found  frequently  as  rolled  pebbles  in 
stream  sands,  where  it  has  been  preserved  on  account  of  its  hard- 
ness. The  ruby  spinels  are  found  in  this  way,  often  associated  with 


MAGNETITE  189 

the  corundum  ruby,  in  the  sands  of  Ceylon,  Siam,  Upper  Burmah, 
Australia  and  Brazil.  Ordinary  spinel  is  found  in  various  localities 
in  New  York,  New  Jersey  and  Massachusetts. 

Use.  When  transparent  and  finely  colored  is  used  as  a  gem. 
Usually  red  in  color  and  known  as  the  spinel  ruby,  balas  ruby, 
etc.  Some  stones  are  blue  in  color.  The  largest  cut  stone 
known  weighs  in  the  neighborhood  of  80  carats.  The  stones 
usually  are  comparatively  inexpensive,  although  a  stone  of  excep- 
tionally fine  color  may  bring  as  high  as  $100  per  carat. 

Gahnite. 

A  zinc  spinel,  ZnAl2O4  or  ZnO.Al2O3,  with  ferrous  iron  and  man- 
ganese isomorphous  with  the  zinc  and  ferric  iron  with  the  aluminium. 
Isometric.  Commonly  octahedral,  also  rarely  showing  dodecahe- 
drons and  cubes.  H.  =7.5-8.  G.  =4.55.  Vitreous  luster.  Dark 
green  color.  Infusible.  The  fine  powder  fused  with  sodium  car- 
bonate on  charcoal  gives  a  white  nonvolatile  coating  of  zinc  oxide. 
A  rare  mineral.  Found  in  the  United  States  in  notable  crystals  at 
Franklin,  New  Jersey,  and  Rowe,  Massachusetts. 

Magnetite. 

Composition.  Fe304  or  FeO.Fe203  =  Iron  sesquioxide  69.0, 
iron  protoxide  31.0  or  oxygen  27.6,  iron  72.4.  The  ferrous  iron 
is  sometimes  replaced  by  magnesium, 
rarely  nickel;  also* at  times  titaniferous. 

Crystallization.  Isometric.  -Octa- 
hedral habit  (Fig.  261),  sometimes 
twinned  octahedrons.  Dodecahedron 
at  times  (Fig.  262)  either  alone  or  with 
octahedron  (Fig.  263) .  Other  forms  rare. 

Structure.     Usually  granular   mas- 
sive, coarse  or  fine;  sometimes  as  sand;  . 
also  frequently  crystallized. 

Physical  Properties.  Often  under  pressure  develops  octahe- 
dral parting.  H.  =  6.  G.  =  5.18.  Metallic  luster.  Color  iron- 
black.  Streak  black.  Strongly  magnetic;  sometimes  a  natural 
magnet,  known  as  lodestone. 


190  MANUAL  OF  MINERALOGY 

Tests.  Infusible.  Slowly  soluble  in  HC1  and  solution  re- 
acts for  both  ferrous  and  ferric  iron.  Distinguished  chiefly  by  its 
strong  magnetism,  its  black  color  and  streak,  and  its  hardness  (6). 


Fig.  262.  Fig.  263. 

Occurrence.  A  common  ore  of  iron.  It  is  found  as  an  accessory 
mineral  in  rocks  of  all  classes  and  sometimes  becomes  their  chief 
constituent.  Most  commonly  associated  with  crystalline  meta- 
morphic  rocks,  also  frequently  in  rocks  that  are  rich  in  ferromagne- 
sium  minerals,  such  as  diabase,  gabbro,  peridotite.  In  many  cases 
forms  large  ore  bodies  that  are  thought  to  be  the  result  of  magmatic 
differentiation;  such  bodies  are  often  highly  titaniferous.  Occurs 
at  times  in  immense  beds  and  lenses,  inclosed  in  old  metamorphic 
rocks.  Found  in  the  black  sands  of  the  seashore.  Occurs  as  thin 
plates  and  dendritic  growths  between  plates  of  mica.  Often  inti- 
mately associated  with  corundum,  forming  the  material  known  as 
emery. 

In  the  United  States,  found  in  large  beds  with  the  Archaean  rocks 
of  the  Adirondacks  in  Warren,  Essex  and  Clinton  counties  of  north- 
ern New  York;  in  various  places  in  New  Jersey;  at  Cornwall, 
Pennsylvania.  Important  foreign  localities  are  in  Norway  and 
Sweden,  where  it  is  the  chief  iron  ore.  Natural  magnets  or  lode- 
stones  are  found  in  Siberia;  in  the  Harz  Mountains,  Germany; 
at  Magnet  Cove,  Arkansas. 

Name.  Probably  derived  from  the  locality  Magnesia,  border- 
ing on  Macedonia.  A  fable,  told  by  Pliny,  ascribes  its  name  to 
a  shepherd  named  Magnes,  who  first  discovered  the  mineral  on 
Mount  Ida  by  noting  that  the  nails  of  his  shoes  and  the  iron 
ferrule  of  his  staff  adhered  to  the  ground. 

Use.     An  important  iron  ore. 


CHROMITE  191 

Franklinite. 

Composition.  (Fe,Zn,Mn)0.(Fe,Mn)203.  Shows  wide  vari- 
ation in  the  proportions  of  the  different  elements  present,  but  con- 
forms to  the  general  formula,  RO.R203. 

Crystallization.  Isometric.  Habit  strongly  octahedral.  Do- 
decahedron sometimes  as  truncations.  Other  forms  rare.  Crys- 
tals often  rounded. 

Structure.  Massive,  coarse  or  fine  granular,  in  rounded  grains 
or  crystallized. 

Physical  Properties.  H.=  6.  G.=  5.15.  Metallic  luster. 
Color  iron-black.  Streak  dark  brown.  Not  magnetic. 

Tests.  Infusible.  Becomes  strongly  magnetic  on  heating  in 
R.  F.  Gives  a  bluish  green  color  to  sodium  carbonate  bead  in 
0.  F.  (manganese) .  When  very  fine  powder  is  mixed  with  sodium 
carbonate  and  heated  intensely  on  charcoal  gives  a  coating  of 
zinc  oxide.  Distinguished  by  above  tests  and  its  black  color 
and  brown  streak. 

Occurrence.  Found  practically  only  in  the  zinc  deposits  at  Frank- 
lin Furnace,  New  Jersey,  which  are  in  the  form  of  large  beds,  in- 
closed in  granular  limestone.  Associated  chiefly  with  zincite  and 
willemite,  with  which  it  is  often  intimately  intergrown. 

Use.  As  an  ore  of  zinc  and  manganese.  The  zinc  is  converted 
into  zinc  white  and  the  residue  is  smelted  to  form  an  alloy  of 
iron  and  manganese,  spiegeleisen,  which  is  used  in  the  manu- 
facture of  steel. 

Chromite. 

Composition.  FeCr204  or  FeO.Cr203  =  Chromium  sesqui- 
oxide  68.0,  iron  protoxide  32.0.  The  iron  may  be  replaced  by 
magnesium  and  the  chromium  by  aluminium  and  ferric  iron. 

Crystallization.  Isometric.  Habit  octahedral.  Crystals  small 
and  rare. 

Structure.     Commonly  massive,  granular  to  compact. 

Physical  Properties.  H.  =  5.5.  G.  =  4.6.  Metallic  to  sub- 
metallic  luster.  Color  iron-black  to  brownish  black.  Streak 
dark  brown. 


192  MANUAL  OF  MINERALOGY 

Tests.  Infusible.  When  finely  powdered  and  fused  on  char- 
coal with  sodium  carbonate  gives  a  magnetic  residue.  Imparts 
a  green  color  to  the  borax  and  salt  of  phosphorus  beads  (chro- 
mium). 

Occurrence.  A  common  constituent  of  peridotite  rocks  and  the 
serpentines  derived  from  them.  One  of  the  first  minerals  to  separate 
from  a  cooling  rock  magma,  and  its  large  ore  deposits  are  thought  to 
have  been  derived  by  such  magmatic  differentiation.  Associated 
with  chrysolite,  serpentine,  corundum,  etc. 

Found  only  sparingly  in  the  United  States.  Pennsylvania,  Mary- 
land, North  Carolina  and  Wyoming  have  produced  it  in  the  past. 
California  is  the  only  producing  state  at  present  (1910).  The 
important  countries  for  its  production  are  New  Caledonia,  Greece 
and  Canada. 

Uses.  Chromium  is  used  with  various  other  metals  to  give 
hardness  to  steel.  Chromite  bricks  are  used  to  a  considerable 
extent  as  linings  for  metallurgical  furnaces,  on  account  of  their 
neutral  and  refractory  character.  The  bricks  are  usually  made 
of  crude  chromite  and  coal  tar  but  sometimes  of  chromite  with 
kaolin,  bauxite,  milk  of  lime  or  with  other  materials.  Chromium 
is  a  constituent  of  certain  green,  yellow,  orange  and  red  pigments 
and  of  similarly  colored  dyes. 


Chrysoberyl. 

Composition.  Beryllium  aluminate,  BeAl204=  Alumina  80.2, 
beryllium  oxide  19.8. 

Crystallization.  Orthorhombic.  Crystals  usually  tabular  par- 
allel to  macropinacoid,  which  face  is  vertically  striated.  Com- 
monly twinned,  often  in  pseudohexagonal  forms. 

Structure.     Usually  in  crystals. 

Physical  Properties.  Prismatic  cleavage.  H.  =  8.5  (un- 
usually high).  G.=  3.65-3.8.  Vitreous  luster.  Color  various 
shades  of  green,  brown,  yellow,  sometimes  red  by  transmitted 
light. 

Tests.  Infusible.  Insoluble.  The  finely  powdered  mineral 
is  wholly  soluble  in  the  salt  of  phosphorus  bead  (absence  of  silica). 
Mineral,  moistened  with  cobalt  nitrate  and  ignited,  turns  blue 


CASSITERITE  193 

(aluminium).     Characterized  by  its  extreme  hardness,  its  yel- 
lowish to  emerald-green  color  and  its  twin  crystals. 

Varieties.  1.  Ordinary.  Color  pale  green,  yellow;  some- 
times transparent. 

2.  Alexandrite.    Emerald-green  variety,  but  red  by  trans- 
mitted light  and  generally  also  by  artificial  light. 

3.  Cat's-eye,  or  Cymophane.    A  variety  which  when  polished 
shows  an  opalescent  luster,  and  across  whose  surface  plays  a 
long  narrow  beam  of  light,  changing  its  position  with  every 
movement  of  the  stone.     This  effect  is  known  as  chatoyancy, 
and  is  best  obtained  when  the  stone  is  cut  in  an  oval  or  round 
form  (en  cabochori).     This  property  of  the  mineral  is  thought 
to  be  due  to  numerous  minute  tubelike  cavities,  arranged  in  a 
parallel  position.     Chrysoberyl  is  the  true  cat's-eye,  and  is  not 
to  be  confused  with  various  other  minerals  possessing  similar 
properties  (e.g.,  quartz). 

Occurrence.  A  rare  mineral.  Found  in  the  alluvial  gem  deposits 
of  Brazil  and  Ceylon;  the  alexandrite  variety  comes  from  the  Ural 
Mountains.  In  the  United  States  it  has  been  found  at  Norway  and 
Stoneham,  Maine;  Haddam,  Connecticut;  and  in  North  Carolina. 

Name.  Chrysoberyl  means  golden  beryl.  Cymophane  is  de- 
rived from  two  Greek  words  meaning  wave  and  to  appear,  in 
allusion  to  the  chatoyant  effect  of  some  of  the  stones.  Alexan- 
drite was  named  in  honor  of  Alexander  II  of  Russia. 

Use.  Serves  as  a  gem  stone.  The  ordinary  yellowish  green 
stones  are  valued  up  to  $5  a  carat.  Alexandrite  brings  as  high 
as  $60  for  a  one-carat  stone.  A  one-carat  cat's-eye  may  have  a 
value  up  to  $50. 

Two  rare  manganese  minerals  belong  in  the  section  of  Inter- 
mediate Oxides:  hausmannite,  MnO.Mn203,  and  braunite,  3Mn203. 
MnSi03. 

4.   DIOXIDES. 
Cassiterite.     Tin  Stone. 

Composition.     Tin  dioxide,  Sn02  =  Oxygen  21.4,  tin  78.6. 
Crystallization.     Tetragonal.    Common  forms  are  prisms  and 
pyramids  of  first  and  second  orders  (Fig.  264).     Frequently  in 


194 


MANUAL  OF  MINERALOGY 


elbow-shaped  twins;    twinning  plane  being  a  pyramid  of  the 
second  order  (Fig.  265). 


a 

m 

Fig.  264. 


Fig.  265. 


Structure.  Usually  massive  granular;  often  in  reniform 
shapes  with  radiating  fibrous-like  structure  (wood  tin) ;  crystal- 
lized. 

Physical  Properties.  H.  =  6-7.  G.=  6.8-7.1  (unusually 
high  for  a  mineral  with  nonmetallic  luster).  Nonmetallic,  ada- 
mantine luster  to  submetallic  and  dull.  Color  usually  brown  or 
black;  rarely  yellow  or  white.  Streak  white. 

Tests.  Infusible.  Gives  globule  of  tin  with  coating  of  white 
tin  oxide  when  finely  powdered  mineral  is  fused  on  charcoal  with 
a  mixture  of  sodium  carbonate  and  charcoal  powder.  Insoluble. 
Recognized  by  its  high  specific  gravity,  its  color  and  light  streak. 

Occurrence.  Cassiterite  is  widely  distributed  in  small  amounts 
but  is  only  produced  on  a  commercial  scale  in  a  few  localities.  Cas- 
siterite has  been  noted  as  an  original  constituent  of  igneous  rocks, 
but  it  is  more  commonly  to  be  found  in  veins  associated  with  quartz. 
As  a  rule  tin-bearing  veins  are  found  in  or  near  pegmatites  or  granitic 
rocks.  Tin  veins  usually  have  minerals  which  contain  fluorine  and 
boron,  such  as  tourmaline,  topaz,  fluorite,  apatite,  etc.,  and  the  min- 
erals of  the  wall  rocks  are  commonly  much  altered.  It  is  thought, 
therefore,  that  the  tin  veins  have  been  formed  through  the  agency 
of  vapors  which  carried  tin  with  boron  and  fluorine.  Cassiterite  is 
at  times  a  minor  constituent  of  pegmatite  veins.  Also  it  is  found 
in  the  form  of  rolled  pebbles  in  placer  deposits. 

Cassiterite  is  not  found  in  large  quantities  in  the  United  States, 
the  only  productive  locality  at  present  being  on  the  Seward  Penin- 
sula, Alaska.  Found  also  in  the  pegmatites  of  North  and  South 


RUTILE 


195 


Carolina;  in  the  Black  Hills,  South  Dakota;  near  El  Paso,  Texas. 
The  world's  supply  of  tin  ore  comes  from  Tasmania,  from  New 
South  Wales,  Queensland  and  other  states  of  Australia,  from  Bolivia 
and  from  the  Malay  States.  Cornwall,  England,  has  produced  large 
amounts  of  tin  ore  in  the  past. 

Use.  Only  ore  of  tin.  Chief  use  of  tin  is  in  coating  or  "tin- 
ning" metals,  particularly  iron,  to  form  what  is  known  as  sheet 
tin.  Tin  is  also  used  in  various  alloys:  solder,  containing  tin 
and  lead;  bell-metal  and  bronze,  containing  copper  and  tin. 

Rutile. 

Composition.  Titanium  dioxide,  Ti02  =  Oxygen  40,  titanium 
60.  A  little  iron  is  usually  present  and  may  amount  to  10  per 
cent. 

Crystallization.  Tetragonal.  Usually  prismatic  with  pyra- 
mid terminations  (Fig.  266).  Vertically  striated.  .Frequently 


Fig.  266. 


Fig.  267. 


Fig.  268. 


in  elbow  twins,  often  repeated  (Figs.  267  and  268).  Twinning 
plane  is  pyramid  of  second  order.  Crystals  sometimes  slender 
acicular. 

Structure.  Usually  crystallized.  Sometimes  compact  mas- 
sive. 

Physical  Properties.  H.=  6-6.5.  G.=  4.18-4.25.  Luster 
adamantine  to  submetallic.  •  Color  red,  reddish  brown  to  black. 
Usually  nearly  opaque,  may  be  transparent. 


196  MANUAL  OF  MINERALOGY 

Tests.  Infusible.  Insoluble.  Fused  with  sodium  carbonate, 
then  fused  mass  dissolved  in  hydrochloric  acid  and  boiled  with 
tin,  the  solution  assumes  a  violet  color. 

Occurrence.  Rutile  is  found  in  granite,  gneiss,  mica  schist,  meta- 
morphic  limestone  and  dolomite,  sometimes  as  an  accessory  mineral 
in  the  rock,  sometimes  in  quartz  veins  traversing  it.  Often  occurs 
as  slender  crystals  penetrating  quartz.  Remarkable  crystals  come 
from  Graves  Mountain,  Lincoln  County,  Georgia.  Also  found  in 
Alexander  County,  North  Carolina,  in  Randolph  County,  Alabama, 
and  at  Magnet  Cove,  Arkansas.  Has  been  mined  near  Roseland, 
Nelson  County,  Virginia.  Notable  European  localities  are  Kragero, 
Norway;  Yrieux,  near  Limoges,  France;  in  the  Ural  Mountains. 

Use.  Source  of  titanium.  Titanium  is  used  to  a  small  extent 
in  steel  and  cast  iron;  for  electrodes  in  arc  lights;  to  give  a  yel- 
low color  to  porcelain  and  false  teeth. 

Octahedrite.     Anatase. 

Titanium  dioxide,  TiC>2,  same  as  rutile  and  brookite.  Tetragonal. 
Usually  in  pyramidal  crystals,  also  tabular  parallel  to  base.  H.  = 
5.5-6.  G.  =  3.8-3.95.  Adamantine  luster.  Color  yellow,  brown, 
blue,  black,  transparent  to  opaque.  Tests  same  as  for  rutile  (which 
see).  A  comparatively  rare  mineral,  found  usually  as  an  accessory 
mineral  in  metamorphic  rocks. 

Brookite. 

Titanium  dioxide,  TiO2,  like  rutile  and  octahedrite.  Orthorhom- 
bic.  Habit  varied.  Tabular  parallel  to  macropinacoid,  square 
prismatic  and  at  times  by  an  equal  development  of  4  prism  and  8 
pyramid  faces  resembles  a  hexagonal  pyramid.  Occurs  only  in  crys- 
tals. H.  =  6.  G.  =  4-4.07.  Luster  adamantine  to  submetallic. 

Color  hair-brown  to  black.  Translucent  to  opaque.  Tests,  same 
as  for  rutile.  A  rare  mineral,  occurring  with  one  of  the  other  forms 
of  titanium  dioxide,  rutile  or  octahedrite.  Occurs  in  good  crystals 
at  St.  Gothard,  Switzerland;  in  the  Tyrol;  Trenadoc,  Wales;  Ellen- 
ville,  New  York;  Magnet  Cove,  Arkansas. 

Pyrolusite. 

Composition.  Manganese  dioxide,  Mn02.  Commonly  con- 
tains a  little  water. 

Crystallization.  Crystals  probably  always  pseudomorphous 
after  manganite. 


PYROLUSITE  197 

Structure.  Radiating  columnar  to  fibrous  (Fig.  A,  pi.  VII); 
also  granular  massive;  often  in  reniform  coats. 

Physical  Properties.  H.  =  2-2.5  (often  soiling  the  fingers). 
G.  =  4.75.  Metallic  luster.  Iron-black  color  and  streak.  Splin- 
tery fracture. 

Tests.  Infusible.  A  small  amount  of  powdered  mineral 
gives  in  0.  F.  a  reddish  violet  bead  with  borax  or  a  bluish  green 
opaque  bead  with  sodium  carbonate.  Gives  oxygen  in  C.  T., 
which  will  cause  a  splinter  of  charcoal  to  ignite  when  placed  in 
tube  above  the  mineral  and  heated.  Only  a  small  amount  of 
water  in  C.  T.  In  hydrochloric  acid,  chlorine  gas  evolved. 

Occurrence.  A  secondary  mineral.  Manganese  is  dissolved  out 
of  the  crystalline  rocks,  in  which  it  is  almost  always  present  in  small 
amounts,  and  redeposited  under  various  conditions,  chiefly  as  pyro- 
lusite.  Dendritic  coatings  of  pyrolusite  are  frequently  observed 
on  rock  surfaces,  coating  pebbles,  etc.  Nodular  deposits  of  pyro- 
lusite are  found  on  the  sea  bottom.  Nests  and  beds  of  manganese 
ores  are  found  inclosed  in  residual  clays,  derived  from  the  decay 
of  manganiferous  limestones.  As  the  rock  has  weathered  and  its 
soluble  constituents -been  taken  away,  the  manganese  content  has 
been  concentrated  in  nodules  and  masses  composed  chiefly  of 
pyrolusite.  Also  found  in  veins  with  quartz  and  various  metallic 
minerals. 

Mined  in  Thuringia,  Moravia,  Transylvania,  Bohemia,  West- 
phalia, Australia,  Japan,  India,  New  Brunswick,  Nova  Scotia.  In 
the  United  States,  manganese  ores  are  found  in  Virginia,  Georgia, 
Arkansas  and  California. 

Name.  Pyrolusite  is  derived  from  two  Greek  words  meaning 
fire  and  to  wash,  because  it  is  used  to  free  glass  through  its  oxidiz- 
ing effect  of  the  colors  due  to  iron. 

Uses.  Most  important  manganese  ore.  Manganese  is  used 
in  the  manufacture  of  the  alloys  with  iron,  spiegekisen  and  ferro- 
manganese,  employed  in  making  steel;  also  in  various  alloys 
with  copper,  zinc,  aluminium,  tin,  lead,  etc.  Pyrolusite  is  used 
as  an  oxidizer  in  the  manufacture  of  chlorine,  bromine  and  oxy- 
gen; as  a  disinfectant  in  potassium  permanganate;  as  a  drier 
in  paints,  a  decolorizer  of  glass,  and  in  electric  cells  and  bat- 
teries. Manganese  is  also  used  as  a  coloring  material  in  bricks, 
pottery,  glass,  etc. 


198  MANUAL  OF  MINERALOGY 

Polianite,  Mn02,  is  a  rare  mineral,  occurring  in  minute  tet- 
ragonal crystals. 

B.   HYDROUS   OXIDES. 

Turgite.     Hydrohematite. 

Composition  is  Fe4O5(OH)2  or  2Fe2O3.lH2O.  Compare  limonite 
and  goethite.  Reniform  and  stalactitic,  with  radiating  fibrous 
structure.  Sometimes  earthy.  H.  =  5.5-6.  G.  =  4.14.  Subme- 
tallic  luster.  Color  black  to  reddish  black.  Streak  Indian-red. 
Difficultly  fusible  at  5-5.5.  Strongly  magnetic  after  heating  in  R.  F. 
In  C.  T.  gives  5  percent  of  water  and  generally  decrepitates.  Dis- 
tinguished from  limonite  by  red  streak  and  from  hematite  by  giving 
water  in  C.  T.  Found  usually  associated  with  limonite.  Occurred 
in  considerable  amount  at  Salisbury,  Conn.,  where  it  often  formed 
an  outer  layer  an  inch  or  more  in  thickness  on  the  masses  of  limonite. 

Diaspore. 

Composition.    AIO(OH)  or  A1203.H20  =  Alumina  85,  water  15. 

Crystallization.  Orthorh.ombic.  Usually  in  thin  crystals, 
tabular  parallel  to  the  brachypinacoid. 

Structure.     Bladed;  foliated  massive. 

Physical  Properties.  Perfect-  cleavage  parallel  to  brachy- 
pinacoid. H.  =  6.5-7.  G.=  3.35-3.45.  Vitreous  luster  except 
on  cleavage  face,  where  it  is  pearly.  Color  white,  gray,  yellowish, 
greenish. 

Tests.  Infusible.  Insoluble.  Fine  powder  wholly  soluble 
in  salt  of  phosphorus  bead  (absence  of  silica).  Ignited  with 
cobalt  nitrate  turns  blue  (aluminium).  Gives  water  in  C.  T. 
Characterized  by  its  good  cleavage,  scaly  structure  and  its 
hardness  (6.5-7). 

Occurrence.  Usually  a  decomposition  product  of  corundum  and 
found  associated  with  that  mineral  in  dolomite,  chlorite-schist,  etc. 
Found  in  the  Urals;  at  Schemnitz,  Hungary;  Campolongo  in  Swit- 
zerland. In  the  United  States  in  Chester  County,  Pennsylvania; 
at  Chester,  Massachusetts;  near  Franklin,  North  Carolina,  etc. 

Name.  Derived  from  a  Greek  word  meaning  to  scatter,  in 
allusion  to  its  decrepitation  when  heated.' 


PLATE  VII. 


A.    Pyrolusite,  Negaunee,  Michigan. 


B.    Manganite,  Ilefeld,  Harz  Mts. 


MANGANITE  199 


Goethite. 

Composition.  FeO(OH)  or  Fe203.H20  =  Oxygen  26,  iron 
62.9,  water  10.1. 

Crystallization.  Orthorhombic.  Prismatic,  vertically  stri- 
ated. Often  flattened  parallel  to  brachypinacoid.  In  acicular 
crystals  at  times. 

Structure.  Massive,  reniform,  stalactitic,  with  radiating 
fibrous  structure.  Foliated.  Rarely  in  distinct  crystals. 

Physical  Properties.  Perfect  cleavage  parallel  to  brachy- 
pinacoid. H.=  5-5.5.  G.  =  4.37.  Adamantine  to  dull  luster. 
Silky  luster  in  certain  fine  scaly  or  fibrous  varieties.  Color 
yellowish  brown  to  dark  brown.  Streak  yellowish  brown  (same 
as  for  limonite). 

Tests.  Difficultly  fusible  (5-5.5).  Becomes  magnetic  in  R.  F. 
Water  in  C.  T.  Told  chiefly  by  the  color  of  its  streak  and  dis- 
tinguished from  limonite  by  its  tendency  to  crystallize  and  the 
smaller  amount  of  water  which  it  contains. 

Occurrence.  Occurs  with  the  other  oxides  of  iron,  hematite  and 
limonite.  Found  at  Eisenfeld  in  Nassau;  near  Bristol,  England; 
at  Lostwithiel,  Cornwall.  In  the  United  States  in  connection  with 
the  Lake  Superior  hematite  deposits,  particularly  at  Negaunee, 
Michigan. 

Use.    A  minor  ore  of  iron. 


Manganite. 

Composition.  MnO(OH)  or  Mn203.H20  =  Oxygen  27.3, 
manganese  62.4,  water  10.3. 

Crystallization.  Orthorhombic.  Crystals  usually  long  pris- 
matic with  obtuse  terminations,  deeply  striated  vertically  (Fig.  B, 
pi.  VII).  Often  twinned. 

Structure.  Usually  in  radiating  masses ;  crystals  often  grouped 
in  bundles.  Also  columnar. 

Physical  Properties.  Perfect  cleavage  parallel  to  brachy- 
pinacoid. H.  =  4.  G.  =  4.3.  Metallic  luster.  Steel-gray  to 
iron-black  color.  Dark  brown  streak. 


200  MANUAL  OF  MINERALOGY 

Tests.  Infusible.  A  small  amount  of  the  powdered  mineral 
gives  in  0.  F.  a  reddish  -violet  bead  with  borax  or  a  bluish  green 
opaque  bead  with  sodium  carbonate.  Much  water  when  heated 
in  C.  T.  Told  chiefly  by  its  black  color,  prismatic  crystals,  hard- 
ness (4)  and  brown  streak.  The  last  two  will  serve  to  distinguish 
it  from  pyrolusite. 

Occurrence.  Found  in  connection  with  pyrolusite  and  other  man- 
ganese minerals  and  with  iron  oxides.  Occurs  at  Ilefeld,  Harz 
Mountains,  in  fine  crystals;  also  at  Ilmenau,  Thuringia;  Cornwall, 
England;  Negaunee,  Michigan,  etc. 

Use.    A  minor  ore  of  manganese. 

Limonite.     Brown  Hematite.     Bog-iron  Ore. 

Composition.  Fe403(OH)6  or  2Fe203.3H20  =  Oxygen  25.7, 
iron  59.8,  water  14.5.  Often  impure.  Compare  turgite  and 
goethite. 

Crystallization.     Noncrystalline. 

Structure.  In  mammillary  to  stalactitic  forms  with  radiat- 
ing fibrous  structure  (Fig.  B,  pi.  II);  also  concretionary;  some- 
times earthy. 

Physical  Properties.  H.  =  5-5.5.  G.  =  3.6-4.  Submetallic 
luster.  Color  dark  brown  to  nearly  black.  Streak  yellowish 
brown. 

Tests.  Difficultly  fusible  (5-5.5).  Strongly  magnetic  after 
heating  in  R.  F.  Much  water  in  C.  T.  (15  per  cent).  Charac- 
terized chiefly  by  its  structure  and  yellow-brown  streak. 

Occurrence.  Limonite  is  a  common  ore  of  iron  and  is  always 
secondary  in  its  origin,  formed  through  the  alteration  or  solution 
of  previously  existing  iron  minerals.  Pyrite  is  often  found  altered 
to  limonite,  the  crystal  form  being  at  times  preserved,  giving  limonite 
pseudomorphs.  Sulphide  veins  are  often  capped  near  the  surface, 
where  oxidation  has  taken  place,  by  a  mass  of  cellular  limonite, 
which  is  known  as  gossan,  or  an  iron  hat.  Iron  minerals  existing  in 
the  rocks  are  among  the  first  to  undergo  decomposition,  and  their 
iron  content  is  often  dissolved  by  percolating  waters  through  the 
agency  of  the  small  amounts  of  carbonic  acid  which  they  contain. 
The  iron  is  transported  as  a  carbonate  by  the  waters  to  the  surface 
and  then  often  carried  by  the  streams  finally  into  marshes  and 
stagnant  pools.  There,  under  the  effect  of  the  evaporation  of  the 


BAUXITE  201 

water  and  its  consequent  loss  of  the  carbonic  acid,  which  served  to 
keep  the  iron  carbonate  in  solution,  and  through  the  agency  of  the 
reducing  action  of  carbonaceous  matter  present,  the  iron  carbonate 
is  changed  to  an  oxide,  which  separates  from  the  water  and  collects 
first  as  an  iridescent  scum  on  the  surface  of  the  water,  and  then  later 
sinks  to  the  bottom.  In  this  way,  under  favorable  conditions,  beds 
of  impure  limonite  can  be  formed  in  the  bottom  of  marshes  and  bogs. 
Such  deposits  are  very  common  and  are  known  as  bog-iron  ores, 
but,  because  of  the  foreign  materials  deposited  along  with  the 
limonite,  are  seldom  of  sufficient  purity  to  be  worked. 

Limonite  deposits  are  also  to  be  found  in  connection  with  iron- 
bearing  limestones.  The  iron  content  of  the  limestone  is  gradually 
dissolved  out  by  circulating  waters  and  transported  by  them  to 
some  favorable  spot,  and  there  the  iron  is  slowly  redeposited  as 
limonite,  gradually  replacing  the  calcium  carbonate  of  the  rock. 
Or,  by  the  gradual  weathering  and  solution  of  the  limestone,  its  iron 
content  may  be  left  in  the  form  of  residual  masses  of  limonite,  lying 
in  clay  above  the  limestone  formation. 

Such  deposits  are  often  of  considerable  size,  and  because  of  their 
greater  purity  are  much  more  often  mined  than  the  bog-iron  ores. 
Deposits  of  this  type  are  to  be  found  chiefly  along  the  Appalachian 
Mountains,  from  western  Massachusetts  as  far  south  as  Alabama. 
These  ores  have  been  of  considerable  importance  in  western  Massa- 
chusetts, northwestern  Connecticut,  southeastern  New  York,  and 
in  New  Jersey.  To-day  they  are  chiefly  mined  in  Alabama,  Virginia, 
Tennessee  and  Georgia.  Limonite  deposits  of  various  kinds  are 
found  throughout  the  western  country,  but  as  yet  they  have  not  been 
extensively  developed. 

Limonite  is  the  coloring  material  of  yellow  clays  and  soils,  and 
mixed  with  fine  clay  makes  what  is  known  as  yellow  ocher.  Limo- 
nite is  commonly  associated  in  its  occurrence  with  hematite,  turgite, 
pyrolusite,  calcite,  siderite,  etc. 

Name.  Derived  from  the  Greek  word  meaning  meadow,  in 
allusion  to  its  occurrence  in  bogs. 

Use.     As  an  iron  ore.     As  a  pigment,  in  yellow  ocher. 

Bauxite. 

Composition.  A120(OH)4  or  A1203.2H20  =  Alumina  73.9, 
water  26.1.  Often  impure. 

Crystallization.     Noncrystalline. 

Structure.  In  round  concretionary  grains;  also  massive, 
earthy,  claylike. 


202  MANUAL  OF  MINERALOGY 

Physical  Properties.  G.  =  2-2.55.  Dull  to  earthy  luster. 
Color  white,  gray,  yellow,  red. 

Tests.  Infusible.  Insoluble.  Assumes  a  blue  color  when 
moistened  with  cobalt  nitrate  and  then  ignited  (aluminium). 
Gives  water  in  C.  T. 

Occurrence.  Probably  usually  a  secondary  mineral  derived  from 
the  decomposition  of  rocks  containing  aluminium  silicates.  Some- 
times as  a  residual  deposit,  preserving  evidences  of  the  original  rock 
structure;  sometimes  oolitic  and  concretionary  in  character  and 
evidently  deposited  from  water.  May,  perhaps,  at  times,  be  de- 
posited by  waters  from  hot  springs.  Occurs  at  Baux,  near  Aries, 
France,  in  disseminated  grains  in  limestone;  at  Allauch,  near  Mar- 
seilles, France,  in  oolitic  form  with  calcite  as  cement.  In  the 
United  States  the  chief  deposits  are  found  in  Georgia,  Alabama  and 
Arkansas. 

Use.  As  an  ore  of  aluminium,  in  the  manufacture  of  alumin- 
ium salts;  artificial  abrasives  and  bauxite  brick. 

Brucite. 

Composition.  Magnesium  hydroxide,  Mg(OH)2  =  Magnesia 
69.0,  water  31.0.  Iron  and  manganese  sometimes  present. 

Crystallization.  Hexagonal-rhombohedral.  Crystals  usu- 
ally tabular  with  prominent  basal  planes,  showing  at  times  small 
rhombohedral  truncations. 

Structure.     Commonly  foliated,  massive. 

Physical  Properties.  Perfect  basal  cleavage.  Folia  flexible 
but  not  elastic.  Sectile.  H.  =  2.5.  G.  =  2.39.  Luster  on  base 
pearly,  elsewhere  vitreous  to  waxy.  Color  white,  gray,  light 
green.  Transparent  to  translucent. 

Tests.  Infusible.  B.  B.  glows.  Gives  water  in  C.  T.  Easily 
soluble  in  hydrochloric  acid,  and  after  solution  has  been  made 
ammoniacal  an  addition  of  sodium  phosphate  gives  a  white 
granular  precipitate  of  ammonium  magnesium  phosphate  (test 
for  magnesium).  Recognized  by  its  foliated  structure,  light 
color  and  pearly  luster  on  cleavage  face.  Distinguished  from 
talc  by  its  greater  hardness  and  lack  of  greasy  feel. 

Occurrence.  Found  associated  with  serpentine,  dolomite,  mag- 
nesite,  chromite,  etc.,  as  a  decomposition  product  of  magnesium 


CARBONATES  203 

silicates.  Notable  localities  for  its  occurrence  are  at  Unst,  one  of 
the  Shetland  Islands;  Aosta,  Italy;  at  Tilly  Foster  Iron  Mine, 
Brewster,  New  York;  at  Wood's  Mine,  Texas,  Pennsylvania.  • 

Gibbsite.     Hydrargillite. 

Aluminium  hydroxide,  A1(OH)3.  Monoclinic.  Rarely  in  hex- 
agonal-shaped tabular  crystals.  Stalactitic  or  botryoidal.  Basal 
cleavage.  H.  =  2-3.5.  G.  =  2.3-2.4.  Luster  pearly,  vitreous  or 
dull.  Color  white.  Infusible.  Insoluble  in  hydrochloric  acid. 
Moistened  with  cobalt  nitrate  and  ignited  assumes  a  blue  color. 
Water  in  C.  T.  A  rare  species,  most  commonly  found  with  corun- 
dum. 

Psilomelane. 

Of  uncertain  composition,  chiefly  manganese  oxides,  MnO2  with 
MnO  and  H^O,  also  small  amounts  of  barium  oxide,  cobalt  oxide, 
etc.  Noncrystalline.  Massive,  botryoidal,  stalactitic.  H.  =  5-6. 
G.  =  3.7-4.7.  Submetallic  luster.  Black  color.  Brownish  black 
streak.  Infusible.  A  small  amount  of  mineral  fused  in  O.  F.  with 
sodium  carbonate  gives  an  opaque  bluish  green  bead.  Gives  much 
water  in  C.  T.  Distinguished  from  the  other  manganese  oxides 
by  its  greater  hardness.  An  ore  of  manganese,  occurring  usually 
with  pyrolusite. 

CARBONATES. 

The  carbonates  are  grouped  into  two  divisions:  (1)  Anhydrous 
Carbonates;  (2)  Add,  Basic  and  Hydrous  Carbonates. 

1.  ANHYDROUS  CARBONATES. 
CALCITE   GROUP. 

The  Calcite  Group  consists  of  a  series  of  carbonates  of  the 
bivalent  metals,  calcium,  magnesium,  ferrous  iron,  manganese 
and  zinc.  They  all  crystallize  in  the  rhombohedral  class  of  the 
Hexagonal  System  with  closely  agreeing  crystal  constants.  They 
all  show  a  perfect  rhombohedral  cleavage,  with  the  angle  between 
the  cleavage  faces  varying  from  105°  to  108°.  The  Calcite 
Group  forms  one  of  the  most  marked  and  important  groups  of 
isomorphous  minerals,  its  chief  members  being  as  follows: 

Calcite,  CaC08. 

Dolomite,  (Ca,Mg)CO,. 


204 


MANUAL  OF  MINERALOGY 


Magnesite,  MgC03. 
Siderite,  FeC03. 
Rhodochrosite,  MnCOs. 
Smithsonite,  ZnC03. 

Calcite. 

Composition.  Calcium  carbonate,  CaC03  =  Carbon  dioxide 
44.0,  lime  56.0.  Small  amounts  of  magnesium,  ferrous  iron, 
manganese  and  zinc  may  replace  the  calcium. 

Crystallization.  Hexagonal-rhombohedral.  Crystals  are  very 
varied  in  habit,  often  highly  complex.  Over  300  different  forms 
have  been  described.  Three  important  habits:  (1)  Prismatic,  in 
which  the  prism  faces  are  prominent,  in  long  or  short  prisms  with 


Fig.  269. 


Fig.  270. 


Fig.  271. 


basal  plane  or  rhombohedral  terminations  (Figs.  273  and  274); 
(2)  Rhombohedral,  in  which  rhombohedral  forms  predominate, 


m 


Fig.  272. 


Fig.  273. 


both  low  and  steep  rhombohedrons,  the  unit  (cleavage)  form  is 
not  common  (Figs.  269,  270,  271  and  272);  (3)  Scalenohedral,  in 
which  the  scalenohedrons  predominate,  often  with  prism  faces 


CALCITE 


205 


and  rhombohedral   truncations    (Figs.  275,  276,  277,  278  and 
A,  pi.  VIII).    All  possible  combinations  and  variations  of  these 


Fig.  275. 


Fig.  276. 


Fig.  277. 


types.  Twinning  according  to  several  different  laws  frequent. 
Fig.  279  represents  one  type  of  twinning  in  which  the  basal 
plane  is  the  twinning  plane. 


Fig.  278. 


Fig.  279. 


Structure.  Crystallized  or  crystalline  granular,  coarse  to  fine. 
Also  fine-grained  to  compact,  earthy.  In  stalactitic  forms,  etc. 

Physical  Properties.  Perfect  cleavage  parallel  to  unit  rhom- 
bohedron  (angle  of  rhombohedron  =  105°  and  75°).  H.=  3. 
G.  =  2.72.  Luster  vitreous  to  earthy.  Color  usually  white  or 
colorless.  May  be  variously  tinted,  gray,  red,  green,  blue, 
yellow,  etc.  Also,  when  impure,  brown  to  black.  Usually 
transparent  to  translucent.  Opaque  when  impure.  Strong 
double  refraction,  hence  the  name  doubly-refracting  spar. 

Tests.  Infusible.  After  intense  ignition,  residue  gives  alka- 
line reaction  to  moistened  test  paper.  Fragment  moistened  with 


206  MANUAL  OF  MINERALOGY 

hydrochloric  acid  and  heated  gives  orange-red  flame.  Frag- 
ments effervesce  freely  in  cold  dilute  hydrochloric  acid.  Concen- 
trated solution  gives  precipitate  of  calcium  sulphate  when  a  few 
drops  of  sulphuric  acid  are  added;  no  precipitate  will  form  if 
solution  is  dilute.  Distinguished  by  its  softness  (3),  its  perfect 
cleavage,  light  color,  vitreous  luster,  etc.  Distinguished  from 
dolomite  by  the  fact  that  fragments  of  calcite  effervesce  freely 
in  cold  hydrochloric  acid,  while  those  of  dolomite  do  not. 

Varieties.  1.  Ordinary.  Calcite  in  cleavable  or  crystalline 
masses.  When  transparent  and  colorless  known  as  Iceland  spar, 
because  of  its  occurrence  in  quantity  in  Iceland. 

2.  Limestone,    Marble,    Chalk.     Calcite    exists    in    enormous 
quantities  in  the  form  of  limestone  rocks,  which  form  a  large 
part  of  the  sedimentary  strata  of  the  earth.     When  these  rock 
masses  have  been  subjected  to  great  heat  and  pressure  they 
develop  a  crystalline  structure,  usually  showing  cleavage  faces 
of  greater  or  less  size.     Crystalline  limestones  are  known  as 
marble.     On  account   of  various   impurities  and   through  the 
presence  in  them  of  other  minerals,  they  assume  a  wide  range  of 
colors,  and  form  a  long  series  of  ornamental  stones  to  which 
various  names  are  given.     Chalk  is  a  very  fine-grained,  pulveru- 
lent deposit  of  calcium  carbonate,  occurring  at  times  in  large 
beds.     It  has  been  formed  through  the  slow  accumulation  on 
the  sea  bottom  of  fragments  of  shells  and  of  the  skeletons  of 
minute  sea  animals. 

3.  Cave  Deposits,  etc.     Calcareous  waters  often  deposit  calcite 
in  the  form  of  stalactites,  concretions,  incrustations,  etc.     It  is 
usually  semitranslucent,  of  light-yellow  colors.     Many  caves  in 
limestone  regions  are  lined  with  such  deposits.     Hot  calcareous 
spring  waters  may  form  a  deposit  of  calcite,  known  as  travertine, 
around  their  mouths.     Such  a  deposit  is  being  formed  at  the 
Mammoth  Hot  Springs,  Yellowstone  Park. 

4.  Siliceous  Calcites.     Calcite  crystals  may  inclose  consider- 
able amounts  of  quartz  sand  (up  to  60  per  cent)  and  form  what 
are  known  as  sandstone  crystals.     Such  occurrences  are  found 
at  Fontainebleau,  France  (Fontainebleau  limestone),  and  in  the 
Bad  Lands,  South  Dakota. 


CALCITE  207 

Occurrence.  Calcite  is  one  of  the  most  common  and  widely 
diffused  of  minerals.  It  occurs  as  enormous  and  widespread  sedi- 
mentary rock  masses,  in  which  it  is  the  predominant,  at  times  prac- 
tically the  only  mineral  present.  Such  rocks  are  the  limestones, 
marbles  (metamorphosed  limestones),  chalks,  calcareous  marls,  cal- 
careous sandstones,  etc.  The  limestone  rocks  have,  in  great  part, 
been  formed  by  the  deposition  on  a  sea  bottom  of  great  thicknesses 
of  calcareous  material  in  the  form  of  shells,  skeletons  of  sea  ani- 
mals, etc.  A  smaller  proportion  of  these  rocks  have  been  formed 
directly  by  precipitation  of  calcium  carbonate.  It  occurs  as  a 
secondary  mineral  in  igneous  rocks  as  a  product  of  decomposition 
of  lime  silicates.  It  is  found  lining  the  amygdaloidal  cavities  in 
lavas.  It  occurs  in  many  sedimentary  and  metamorphic  rocks  in 
greater  or  less  proportion.  It  is  the  cementing  material  in  the  light- 
colored  sandstones.  Calcite  is  also  one  of  the  most  common  of 
vein  minerals,  occurring  as  a  gangue  material,  with  all  sorts  of 
metallic  ores. 

It  would  be  quite  impossible  to  specify  all  of  the  important  dis- 
tricts for  the  occurrence  of  calcite  in  its  various  forms.  Some  of 
the  more  notable  localities  in  which  finely  crystallized  calcite  is 
found  are  as  follows:  Andreasberg  in  the  Harz  Mountains;  various 
places  in  Saxony;  in  Cumberland,  Derbyshire,  Devonshire,  Corn- 
wall, Lancashire,  England;  Iceland;  Guanajuato,  Mexico;  Joplin, 
Missouri;  Lake  Superior  copper  district;  Rossie,  New  York,  etc. 

Use.  The  most  important  use  for  calcite  is  for  the  manu- 
facture of  lime  for  mortars  and  cements.  Limestone  when 
heated  to  about  1000°  F.  loses  its  carbonic  acid,  and  is  converted 
.into  quicklime,  CaO.  This,  when  mixed  with  water  (staked 
lime),  swells,  gives  off  much  heat,  and  finally  by  absorption  of 
carbon  dioxide  from  the  air  hardens,  or,  as  commonly  termed, 
"sets."  Quicklime  when  mixed  with  sand  forms  the  common 
mortar  used  in  building.  Certain  limestones  contain  various 
clayey  materials  as  impurities.  Cements  made  from  these  lime- 
stones have  the  valuable  property  of  hardening  under  water, 
and  are  known  as  hydraulic  cements.  Many  hydraulic  cements 
are  made  up  artificially  by  combining  their  ingredients  in  experi- 
mentally determined  proportions.  The  chemistry  of  the  process 
of  their  hardening  is  not  fully  understood,  but  various  silicates 
of  calcium  and  aluminium  are  probably  formed.  Portland 
cement,  used  so  largely  in  concrete  construction,  is  a  mixture 
of  about  6  parts  of  lime,  2  parts  of  silica,  and  1  part  of  alumina. 


208 


MANUAL  OF  MINERALOGY 


Chalk  is  used  as  a  fertilizer,  for  whiting  and  whitewash,  for 
crayons,  etc.  It  is  found  in  many  places  in  Europe,  the  chalk 
cliffs  of  Dover  being  famous. 

Limestone  is  largely  used  as  a  building  material,  and  is  ob- 
tained in  the  United  States  chiefly  from  Pennsylvania,  Indiana, 
Ohio,  Illinois,  New  York,  Missouri,  Wisconsin.  Limestone  is 
largely  used  as  a  flux  for  smelting  various  metallic  ores.  A 
fine-grained  limestone  is  used  in  lithographing. 

Marbles  are  used  very  extensively  as  ornamental  and  building 
material.  The  most  important  marble  quarries  in  the  United 
States  are  found  in  Vermont,  New  York,  Georgia,  Tennessee,  etc. 

Iceland  spar  is  valuable  for  optical  instruments,  being  used  in 
the  form  of  the  Nicol  prism  to  produce  polarized  light.  Obtained 
at  present  only  from  Iceland. 

Dolomite. 

Composition.  Carbonate  of  calcium  and  magnesium, 
CaMg(C03)2  =  Carbon  dioxide  47.8,  lime  30.4,  magnesia  21.7. 
Varieties  occur  in  which  the  proportion  of  CaC03  to  MgC03 
is  not  as  1  :  1.  Small  amounts  of  ferrous  carbonate  frequently 
replace  some  of  the  magnesium  carbonate.  Manganese  is  also 
present  at  times. 


Fig.  280. 


Fig.  281. 


Crystallization.  Hexagonal-rhombohedral.  Crystals  are 
usually  the  unit  rhombohedron  (cleavage  rhombohedron)  (Fig. 
280).  Faces  often  curved,  and  sometimes  so  acutely  as  to  form 
"saddle-shaped"  crystals  (Fig.  281).  Other  forms  rare. 

Structure.  In  coarse,  granular,  cleavable  masses  to  fine- 
grained and  compact  and  in  crystals. 


PLATE  VIII. 


B.    Aragonite,  Cleator  Moor,  England. 


MAGNESITE  209 

Physical  Properties.  Perfect  rhombohedral  cleavage  (cleav- 
age angle  =  106°  15').  H.  =  3:5-4.  G.  =  2.85.  Vitreous  lus- 
ter; pearly  in  some  varieties  (pearl  spar).  Color  usually  some 
shade  of  pink,  flesh  color;  may  be  colorless,  white,  gray,  green, 
brown  and  black.  Transparent  to  translucent. 

Tests.  Infusible.  After  intense  ignition  a  fragment  will  give 
an  alkaline  reaction  to  moistened  test  paper.  Readily  soluble, 
with  effervescence  in  hot  hydrochloric  acid;  fragment  only  slowly 
attacked  by  cold  dilute  acid  (difference  from  calcite).  Solution 
oxidized  by  nitric  acid  and  then  made  ammoniacal  (may  pre- 
cipitate ferric  hydroxide)  will  with  ammonium  oxalate  give  a 
white  precipitate  of  calcium  oxalate;  nitrate  with  sodium  phos- 
phate gives  granular  white  precipitate  of  ammonium  magnesium 
phosphate.  Crystallized  variety  told  by  its  curved  rhombohe- 
dral crystals  and  usually  by  its  flesh-pink  color. 

Occurrence.  Dolomite  occurs  chiefly  in  widely  extended  rock 
masses  as  dolomite  limestone  and  marble.  Occurrence  same  as  for 
calcite  rocks.  The  two  varieties  can  only  be  told  apart  by  tests, 
the  simplest  being  to  see  if  a  drop  of  cold  hydrochloric  acid  placed 
on  the  rock  will  produce  effervescence  (if  so,  rock  is  calcite;  if  not, 
dolomite).  Often  intimately  mixed  with  calcite.  Occurs  also  as  a 
vein  mineral,  chiefly  in  the  lead  and  zinc  veins  that  traverse  lime- 
stone. Found  in  large  rock  strata  in  the  dolomite  region  of  southern 
Tyrol;  Binnenthal,  Switzerland;  northern  England;  Joplin,  Mis- 
souri, etc. 

Use.  As  a  building  and  ornamental  stone.  For  the  manu- 
facture of  certain  cements.  For  the  manufacture  of  magnesia 
used  in  the  preparation  of  refractory  linings  of  the  converters  in 
the  basic  steel  process. 

Ankerite,  CaC03.(Mg,Fe,Mn)C03,  is  a  subspecies  interme- 
diate between  calcite,  dolomite  and  siderite. 

Magnesite. 

Composition.  Magnesium  carbonate,  MgC03  =  Carbon  di- 
oxide 52.4,  magnesia  47.6.  Iron  carbonate  also  often  present. 

Crystallization.  Hexagonal-rhombohedral.  In  rhombohe- 
dral crystals. 


210  MANUAL  OF  MINERALOGY 

Structure.  Compact  earthy  forms  common,  also  less  fre- 
quently in  cleavable  granular  masses,  coarse  to  fine.  Also  com- 
pact. Crystals  rare. 

Physical  Properties.  Perfect  rhombohedral  cleavage,  some- 
times distinct.  H.  =  3.5-4.5.  G.  =  3-3.1.  Vitreous  luster. 
Color  white,  gray,  yellow,  brown.  Transparent  to  opaque. 

Tests.  Infusible.  After  intense  ignition  gives  a  faint  alkaline 
reaction  on  moistened  test  paper.  Scarcely  acted  upon  by  cold 
but  dissolves  with  effervescence  in  hot  hydrochloric  acid.  Solu- 
tion, after  the  precipitation  of  any  iron  and  calcium,  gives  in 
the  presence  of  an  excess  of  ammonia,  with  sodium  phosphate,  a 
white  granular  precipitate  of  ammonium  magnesium  phosphate. 

Occurrence.  Found  associated  with  serpentine  rocks  as  a  product 
of  their  alteration,  with  dolomite,  brucite,  etc.  Magnesite  is  mined 
to  a  small  extent  in  Tulare  County,  California.  Most  of  the  mag- 
nesite  used  in  the  United  States  is  imported,  coming  chiefly  from 
Stryia  in  Austria-Hungary  and  from  Greece. 

Use.  Magnesite  is  chiefly  used  in  the  preparation  of  mag- 
nesite  bricks  for  refractory  linings  in  metallurgical  furnaces. 
Also  used  in  the  preparation  of  magnesium  salts  (Epsom  salts, 
magnesia,  etc.). 

Siderite.     Spathic  Iron.     Chalybite. 

Composition.  Ferrous  carbonate,  FeC03  =  Carbon  dioxide 
37.9,  iron  protoxide  62.1,  iron  =  48.2.  Manganese,  magnesium 
and  calcium  may  be  present  in  small  amounts. 

Crystallization.  Hexagonal-rhombohedral.  Crystals  usually 
unit  rhombohedrons  (same  as  cleavage  form),  frequently  with 
curved  faces. 

Structure.  Usually  cleavable  granular.  At  times  botryoidal, 
compact  and  earthy.  More  rarely  in  crystals. 

Physical  Properties.  Perfect  rhombohedral  cleavage  (cleav- 
age angle  =  107°).  H.  =  3.5-4.  G.  =  4.5-5.  Vitreous  luster. 
Color  usually  light  to  dark  brown.  Transparent  to  opaque. 

Tests.  Difficultly  fusible  (4.5-5).  Becomes  strongly  mag- 
netic on  heating.  Heated  in  C.  T.  decomposes  and  gives  a 
black  magnetic  residue.  Soluble  in  hydrochloric  acid  with 


RHODOCHROSITE  211 

effervescence;  solution  gives  with  potassium  ferricyanide  a  dark 
blue  precipitate  (test  for  ferrous  iron).  Recognized  usually  by 
its  color  and  cleavage. 

Varieties.  1.  Crystallized.  In  crystals  or  granular  cleavable 
masses. 

2.  Concretionary.     In  globular  concretions. 

3.  Clay  Ironstone.     Impure  by  admixture  with  clay  materials. 
Sometimes  in  concentric  layers.     Forms  stratified  bodies  with 
coal  formations,  etc. 

4.  Black-band  Ore.    An  impure  stratified  deposit  of  siderite, 
containing  considerable  carbonaceous  matter.    Associated  with 
coal  beds. 

Occurrence.  Found  in  the  form  of  clay  ironstone  and  black-band 
ore  in  extensive  stratified  formations  associated  with  coal  measures. 
These  ores  are  the  chief  source  of  iron  in  Great  Britain  and  are  found 
in  Staffordshire,  Yorkshire  and  Wales.  Clay  ironstone  is  also  abun- 
dant in  the  coal  measures  of  western  Pennsylvania  and  eastern  Ohio, 
but  it  is  not  used  to  any  great  extent  as  an  ore.  Siderite,  in  its 
crystallized  form,  is  a  common  vein  mineral  associated  with  various 
metallic  ores,  as  silver  minerals,  pyrite,  chalcopyrite,  tetrahedrite, 
galena,  etc. 

Name.  The  original  name  for  the  mineral  was  spherosiderite, 
given  to  the  concretionary  variety  and  subsequently  shortened 
to  siderite  to  apply  to  the  entire  species.  Spathic  ore  is  a  com- 
mon name.  Chalybite,  used  by  some  mineralogists,  was  derived 
from  the  Chalybes,  who  lived  on  the  Black  Sea,  and  were  in 
ancient  times  workers  in  iron. 

Use.  An  ore  of  iron.  Important  in  Great  Britain,  but  of 
very  subordinate  value  in  the  United  States. 

Rhodochrosite. 

Composition.  Manganese  protocarbonate,  MnC03  =  Carbon 
dioxide  38.3,  manganese  protoxide  61.7.  Iron  is  usually  pres- 
ent, replacing  a  part  of  the  manganese  and  sometimes  calcium, 
magnesium,  zinc,  etc. 

Crystallization.  Hexagonal -rhombohedral.  Crystals  unit 
rhombohedrons  (same  as  cleavage  rhombohedron),  frequently 
with  curved  faces. 


212  MANUAL  OF  MINERALOGY 

Structure.  Usually  cleavable  massive;  granular  to  compact. 
Rarely  in  crystals. 

Physical  Properties.  Perfect  rhombohedral  cleavage  (cleav- 
age angle  =  107°).  H.  =  3.5-4.5.  G.  =  3.45-3.6.  Vitreous 
luster.  Color  usually  some  shade  of  rose-red;  may  be  light  pink 
to  dark  brown.  Transparent  to  translucent. 

Tests.  Infusible.  Soluble  in  hot  hydrochloric  acid  with 
effervescence.  Gives  reddish  violet  color  to  borax  bead  when 
heated  in  0.  F.  Told  usually  by  its  pink  color,  rhombohedral 
cleavage  and  hardness  (4).  Distinguished  by  its  hardness  from 
rhodonite  (MnSi03)  (H.  =  5.5-6.5). 

Occurrence.  A  comparatively  rare  mineral,  occurring  in  veins 
with  ores  of  silver,  lead  and  copper,  and  with  other  manganese 
minerals.  Found  in  the  silver  mines  of  Hungary  and  Saxony.  In 
the  United  States  at  Branch ville,  Connecticut;  Franklin,  New 
Jersey;  in  good  crystals  at  Alicante,  Colorado,  etc. 

Name.     Derived  from  two  Greek  words  meaning  rose  and 
color,  in  allusion  to  its  rose-pink  color. 
Use.    A  minor  ore  of  manganese. 


Smithsonite. 

Composition.  Zinc  carbonate,  ZnC03  =  Carbon  dioxide  35.2, 
zinc  protoxide  64.8.  Iron  and  manganese  often  replace  a  part 
of  the  zinc;  also  at  times  calcium  and  magnesium. 

Crystallization.  Hexagonal-rhombohedral.  Rarely  in  small 
rhombohedral  or  scalenohedral  crystals. 

Structure.  Usually  reniform,  botryoidal  or  stalactitic  and  in 
crystalline  incrustations  or  in  honeycombed  masses  known  as 
dry-bone  ore.  Also  granular  to  earthy.  Distinct  crystals  rare. 

Physical  Properties.  Perfect  rhombohedral  cleavage,  which, 
on  account  of  the  usual  structure,  is  seldom  observed.  H.  =  5 
(unusually  high  for  a  carbonate).  G.  =  4.30-4.35.  Vitreous 
luster.  Color  usually  dirty  brown.  May  be  white,  green,  blue, 
pink,  etc.  Translucent  to  opaque. 

Tests.  Infusible.  Soluble  in  hydrochloric  acid  with  effer- 
vescence. A  fragment  heated  B.  B.  in  R.  F.  gives  bluish  green 


ARAGONITE  GROUP  213 

streaks  in  the  flame,  due  to  the  burning  of  the  volatilized  zinc. 
Heated  in  R.  F.  on  charcoal  gives  a  nonvolatile  coating  of  zinc 
oxide,  yellow  when  hot,  white  when  cold;  if  coating  is  moistened 
with  cobalt  nitrate  and  again  heated  it  turns  green.  Distin- 
guished by  its  effervescence  in  acids,  its  tests  for  zinc,  its  hard- 
ness (5)  and  its  high  specific  gravity. 

Occurrence.  It  is  a  zinc  ore  of  secondary  origin.  Found  in  con- 
nection with  zinc  deposits  near  the  surface,  and  where  the  oxidized 
ores  have  been  acted  upon  by  carbonated  waters.  Common  in 
connection  with  zinc  deposits  lying  in  limestone  rocks.  Associated 
with  sphalerite,  galena,  calamine,  cerussite,  calcite,  limonite,  etc. 
Often  found  in  pseudomorphs  after  calcite.  "Dry-bone  ore"  is  a 
honeycombed  mass,  with  the  appearance  of  dried  bone,  whose 
structure  has  resulted  from  the  manner  of  deposition  of  the  mineral. 
Some  calamine,  the  silicate  of  zinc,  is  included  under  the  term. 
Occurs,  as  an  ore,  in  the  zinc  deposits  of  Missouri,  Arkansas,  Wis- 
consin, Virginia,  etc.  Found  at  times  in  translucent  green  or 
greenish  blue  material  which  is  available  for  ornamental  uses.  Such 
smithsonite  is  found  at  Laurium,  Greece,  and  at  Kelly,  New  Mexico. 

Name.  Named  in  honor  of  James  Smithson  (1754-1829), 
who  founded  the  Smithsonian  Institution  at  Washington.  Eng- 
lish mineralogists  call  the  mineral  calamine,  using  either  electric 
calamine  or  hemimorphite  as  the  name  for  the  silicate. 

Use.    An  ore  of  zinc. 


ARAGONITE   GROUP. 

The  Aragonite  Group  consists  of  a  series  of  carbonates  of  the 
bivalent  metals,  calcium,  strontium,  barium  and  lead,  which 
crystallize  in  the  Orthorhombic  System  with  closely  related  crys- 
tal constants  and  similar  habits  of  crystallization.  All  of  them 
appear  at  times  in  twin  crystals  which  are  pseudohexagonal  in 
character.  The  members  of  the  group  are: 

Aragonite,  CaC03. 
Strontianite,  SrC08. 
Witherite,  BaC08. 
Cerussite,  PbCO,. 


214 


MANUAL  OF  MINERALOGY 


Aragonite. 

Composition.  Calcium  carbonate,  like  calcite,  CaC03  =  Car- 
bon dioxide  44,  lime  56.  May  contain  a  little  strontium  or  lead, 
rarely  zinc. 

Crystallization.  Orthorhombic.  Three  prominent  habits  of 
crystallization:  (1)  Acicular  pyramidal;  consisting  of  a  prism 
terminated  by  a  combination  of  a  very  steep  pyramid  and 
brachydome  (see  Fig.  282;  and  B,  pi.  VIII).  Usually  in  radi- 
ating groups  of  large  to  very  small  crystals.  (2)  Tabular;  con- 
sisting of  prominent  brachypinacoid  faces  modified  by  a  prism 


rA 


Fig.  282. 


Fig.  283. 


Fig.  284. 


Fig.  285. 


and  a  low  brachydome  (Fig.  283) .  Often  twinned  with  a  prism 
face  as  a  twinning  plane  (Fig.  284).  (3)  In  pseudohexagonal 
twins  (Fig.  285).  This  type  shows  a  hexagonal-like  prism  ter- 
minated by  a  basal  plane,  and  is  formed  by  an  intergrowth  of 
three  individuals  with  basal  planes  in  common  and  their  prism 
faces  falling  partly  in  the  same  plane,  and  partly  with  only 
slightly  different  positions.  The  crystals  are  distinguished  from 
true  hexagonal  forms  by  noting  that  the  basal  plane  is  striated 
in  three  different  directions,  and  also  by  the  fact  that,  because 
the  prism  angle  of  the  simple  crystals  is  not  exactly  60°,  the 
composite  prism  faces  for  the  twin  will  often  show  slight  re- 
entrant angles. 

Structure.    In  crystals.    Also  reniform,  columnar,  stalactitic, 
etc. 


WITHERITE  215 

Physical  Properties.  Vitreous  luster.  Colorless,  white,  pale 
yellow  and  variously  tinted.  Transparent  to  translucent.  H.= 
3.5-4.  G.=  2.95  (harder  and  heavier  than  calcite). 

Tests.  Infusible.  Decrepitates.  After  intense  ignition  the 
powder  gives  an  alkaline  reaction  on  moistened  test  paper. 
Fragments  fall  to  powder  (change  to  calcite)  when  heated  at  low 
redness  in  C.  T.  Chemical  tests  same  as  for  calcite  (page  205). 
Distinguished  from  calcite  by  its  lack  of  cleavage,  and  the  fact 
that  fragments  fall  to  powder  when  heated  in  C.  T. 

Occurrence.  Less  stable  than  calcite  and  much  less  common  in 
its  occurrence.  Usually  found  as  a  vein  mineral.  Experiments  have 
shown  that  carbonated  waters  containing  calcium  more  often  deposit 
aragonite  when  they  are  hot  and  calcite  when  they  are  cold.  Some  sea 
shells  are  composed  entirely  or  in  part  of  aragonite.  The  pearly  layer 
of  many  shells  is  aragonite.  It  has  been  noted  that  the  aragonite 
shells  are  not  readily  preserved  as  fossils,  being  easily  dissolved  or 
disintegrated,  or  at  times  apparently  slowly  changing  to  calcite. 
Aragonite  is  most  commonly  found  associated  with  beds  of  gypsum  and 
deposits  of  iron  ore  (where  it  sometimes  occurs  in  forms  resembling 
coral,  and  is  called  flos  Jerri,  flower  of  iron).  At  times  found  lining 
amygdaloidal  cavities  in  basalt.  Found  frequently  with  pyrite, 
chalcopyrite,  galena,  malachite,  etc.  Notable  localities  for  the 
various  crystalline  types  are  as  follows:  Pseudohexagonal  twin 
crystals  are  found  at  Aragon,  Spain;  Bastennes,  in  the  south  of 
France;  and  at  Girgenti,  Sicily.  The  tabular  type  of  crystals  is 
found  near  Bilin,  Bohemia.  The  acicular  type  is  found  at  Alston 
Moor  and  Cleator,  Cumberland,  England.  Flos  ferri  is  found  in 
the  Stryian  iron  mines.  Stalactitic  forms  occur  in  Buckingham- 
shire and  Devonshire,  England,  and  Lanarkshire,  Scotland.  A 
fibrous  banded  form  of  a  delicate  blue  color  comes  from  Chile. 

Witherite. 

Composition.  Barium  carbonate,  BaC03  = 
Carbon  dioxide  22.3,  barium  oxide  77.7. 

Crystallization.  Orthorhombic.  Crystals 
always  twinned,  forming  pseudohexagonal  pyra- 
mids by  the  intergrowth  of  three  individuals 
terminated  by  brachy domes  (Fig.  286).  Crys- 
tals sometimes  doubly  terminated ;  often  deeply 
striated  horizontally  and  by  a  series  of  re-  Fig.  286. 


216  MANUAL  OF  MINERALOGY 

entrant  angles  have  the  appearance  of  one  pyramid  capping 
another. 

Structure.  In  twin  crystals,  also  botryoidal  to  globular; 
columnar  or  granular. 

Physical  Properties.  H.  =  3.5.  G.  =  4.3.  Vitreous  luster. 
Colorless,  white,  gray.  Translucent. 

Tests.  Easily  fusible  at  2.5-3,  giving  a  yellowish  green  flame 
(barium).  After  intense  ignition  gives  an  alkaline  reaction  on 
moistened  test  paper.  Soluble  in  hydrochloric  acid  with  effer- 
vescence. All  solutions,  even  the  very  dilute,  give  precipitate  of 
barium  sulphate  with  sulphuric  acid  (difference  from  calcium 
and  strontium).  Heavy. 

Occurrence.  A  comparatively  rare  mineral.  Found  in  fine  crys- 
tals at  Hexham  in  Northumberland  and  Alston  Moor  in  Cumber- 
land. Occurs  at  Tarnowitz  in  Silesia;  Leogang  in  Salzburg;  near 
Lexington,  Kentucky;  Thunder  Bay,  Lake  Superior. 

Use.    A  minor  source  of  barium  compounds. 


Strontianite. 

Composition.  Strontium  carbonate,  SrC03  =  Carbon  dioxide 
29.9,  strontia  70.1.  A  little  calcium  sometimes  present. 

Crystallization.  Orthorhombic.  Crystals  usually  acicular, 
like  type  (1)  under  aragonite.  Twinning  also  frequent,  giving 
at  times  pseudohexagonal  forms. 

Structure.  Radiating  crystallized,  also  columnar;  fibrous 
and  granular. 

Physical  Properties.  H.=  3.5-4.  G.=  3.7.  Vitreous  luster. 
White,  gray,  yellow,  green.  Transparent  to  translucent. 

Tests.  Infusible.  On  intense  ignition  throws  out  fine 
branches  and  gives  a  crimson  flame  (strontium)  and  residue 
gives  alkaline  reaction  on  moistened  test  paper.  Effervescence 
in  hydrochloric  acid,  and  the  mediumly  dilute  solution  will  give 
precipitate  of  strontium  sulphate  on  addition  of  a  few  drops  of 
sulphuric  acid;  no  precipitate  will  form  in  the  very  dilute  solu- 
tion (difference  from  calcium  and  barium).  Usually  necessary 
to  make  the  above  tests  to  determine  the  mineral. 


PLATE  IX. 


Cerussite,  Broken  Hill,  New  South  Wales. 


CERUSSITE 


217 


Occurrence.  A  comparatively  rare  mineral.  Originally  found 
at  Strontian  in  Argyllshire.  Occurs  also  with  lead  ores  at  Pateley 
Bridge  Yorkshire;  at  Hamm  and  Miinster,  Westphalia;  at  Schoharie, 
New  York,  etc. 

Use.  Has  no  great  commercial  use.  A  minor  source  of  stron- 
tium compounds,  used  in  fireworks  and  in  the  separation  of 
sugar  from  molasses. 

Cerussite. 

Composition.  Lead  carbonate,  PbC03  =  Carbon  dioxide 
16.5,  lead,  oxide  83.5. 

Crystallization.  Habit  varied  and  crystals  show  many  forms. 
Crystals  often  tabular  parallel  to  brachy- 
pinacoid  (Fig.  287).  Frequently  twinned, 
forming  lattice-like  groups  with  the  plates 
crossing  each  other  at  60°  angles  (pi.  IX). 
Sometimes  pyramidal  in  habit;  also  twinned 
in  pseudohexagonal  pyramids,  frequently 
with  deep  reentrant  angles  in  the  prism 
zone. 

Structure.  In  crystals  or  in  granular 
crystalline  aggregates;  fibrous;  granular 
massive;  compact;  earthy. 

Physical  Properties.  H.=  3-3.5.  G.=  6.55  (high  for  a 
mineral  with  nonmetallic  luster).  Adamantine  luster.  Color- 
less, white  or  gray.  Transparent  to  almost  opaque. 

Tests.  Easily  fusible  (1.5).  With  sodium  carbonate  B.  B. 
on  charcoal  gives  globule  of  lead  and  yellow  to  white  coating  of 
lead  oxide.  Soluble  in  warm  dilute  nitric  acid  with  effervescence. 
In  C.  T.  usually  decrepitates  and  is  changed  to  lead  oxide,  which 
is  dark  yellow  when  hot.  Recognized  by  its  high  specific  gravity, 
white  color  and  adamantine  luster. 

Occurrence.  An  important  and  widely  distributed  lead  ore  of 
secondary  origin,  formed  by  the  oxidation  of  galena  in  the  presence 
of  carbonated  waters.  Found  in  the  upper  and  oxidized  zone  of 
lead  veins,  associated  with  galena,  anglesite,  sphalerite,  smithsonite, 
silver  ores,  etc.  Notable  localities  for  its  occurrence  are  Ems  in 
Nassau;  Mies,  Bohemia;  Nerchinsk,  Siberia;  Broken  Hill,  New 


Fig.  287. 


218  MANUAL  OF  MINERALOGY 

South    Wales;    Phoenix ville,    Pennsylvania;    Leadville,    Colorado, 
various  districts  in  Arizona,  etc. 

Use.    An  important  ore  of  lead. 


Phosgenite,  a  chlorocarbonate  of  lead  (PbCl)2C03,  tetragonal 
in  crystallization,  is  a  rare  member  of  the  Anhydrous  Carbonate 
Division. 

2.  ACID,   BASIC  AND  HYDROUS   CARBONATES. 
Malachite.     Green  Copper  Carbonate. 

Composition.  Basic  carbonate  of  copper,  (Cu.OH)2C03  or 
CuC03.Cu(OH)2  =  Carbon  dioxide  19.9,  cupric  oxide  71.9,  water 
8.2.  Copper  =  57.4. 

Crystallization.  Monoclinic.  Crystals  usually  slender  pris- 
matic but  seldom  distinct. 

Structure.  Usually  radiating  fibrous  with  botryoidal  or  stal- 
actitic  structure  (see  Fig.  C,  pi.  III).  Often  granular  or  earthy. 

Physical  Properties.  Perfect  basal  cleavage.  H.  =  3.5-4. 
G.  =  3.9-4.03.  Adamantine  to  vitreous  luster  in  crystals;  often 
silky  in  fibrous  varieties;  dull  in  earthy  type.  Color  bright  green. 
Translucent  to  opaque. 

Tests.  Fusible  (3),  giving  a  green  flame.  With  fluxes  in  R.  F. 
on  charcoal  gives  copper  globule.  Soluble  in  hydrochloric  acid 
with  effervescence.  Solution  turns  deep  blue  with  excess  of 
ammonia.  Much  water  in  C.  T.  .Recognized  by  its  bright 
green  color  and  radiating  fibrous  structure. 

Occurrence.  An  important  and  widely  distributed  copper  ore  of 
secondary  origin.  Found  in  the  oxidized  portions  of  copper  veins 
associated  with  azurite,  cuprite,  native  copper,  iron  oxides  and  the 
various  sulphides  of  copper  and  iron.  Usually  occurs  in  copper 
veins  that  lie  in  limestones.  Notable  localities  for  its  occurrence 
are  at  Nizhni  Tagilsk  in  the  Ural  Mountains;  at  Bembe  on  west 
coast  of  Africa;  in  the  copper  mines  in  Chile;  in  New  South  Wales. 
In  the  United  States,  an  important  copper  ore  in  the  southwestern 
copper  districts;  at  Bisbee,  Morenci,  and  other  localities  in  Arizona; 
in  New  Mexico;  at  Cannanea,  in  northern  Mexico. 


GAY-LUSSITE  219 

Name.  Derived  from  the  Greek  word  for  mallows,  in  allusion 
to  its  green  color. 

Use.  An  important  ore  of  copper.  Has  been  used  to  some 
extent  as  an  ornamental  material  for  vases,  veneer  for  table  tops, 
etc. 

Azurite.     Chessylite.     Blue  Copper  Carbonate. 

Composition.  A  basic  carbonate  of  copper,  Cu(Cu.OH)2(C03)2 
or  2CuC03.Cu(OH)2  =  Carbon  dioxide  25.6,  cupric  oxide  69.2, 
water  5.2.  Copper  =  55.3. 

Crystallization.  Monoclinic.  Habit  varied.  Crystals  fre- 
quently complex  and  distorted  in  development,  sometimes  in 
radiating  spherical  groups. 

Structure.  Crystallized.  In  radiating  botryoidal  structure. 
Earthy. 

Physical  Properties.  H.  =  3.5-4.  G.  =  3.77.  Vitreous  lus- 
ter. Intense  azure-blue  color.  Transparent  to  opaque. 

Tests.  Same  as  for  malachite  (which  see).  Characterized 
chiefly  by  its  azure-blue  color. 

Occurrence.  Origin  and  associations  same  as  for  malachite. 
Found  in  fine  crystals  at  Chessy,  France;  in  Siberia;  at  Copper 
Queen  Mine,  Bisbee,  Arizona.  Widely  distributed  with  copper 
ores.  Not  so  common  as  malachite. 

Name.     Named  in  allusion  to  its  color. 
Use.     An  important  ore  of  copper. 

Aurichalcite. 

A  basic  carbonate  of  zinc  and  copper,  2(Zn,Cu)CO3.3(Zn,Cu)(OH)2. 
In  acicular  crystals,  forming  drusy  incrustations.  H=  2.  G.  = 
3.6.  Pearly  luster.  Color  pale  green  to  blue.  Infusible.  Soluble 
in  hydrochloric  acid  with  effervescence.  Solution  turns  blue  with 
ammonia  in  excess.  Fused  in  R.  F.  on  charcoal  with  sodium  car- 
bonate gives  a  nonvolatile  coating  of  zinc  oxide  (yellow  when  hot, 
white  when  cold).  Water  in  C.  T.  A  rare  mineral,  found  in  the 
oxidized  zones  of  copper  veins. 

Gay-Lussite. 

A  hydrous  carbonate  of  calcium  and  sodium,  CaCO3.Na2CO3.5H2O. 
Monoclinic.  In  rude  crystals  with  uneven  surfaces.  Often  wedge- 


220  MANUAL  OF  MINERALOGY 

shaped.  Prismatic  cleavage.  H.  =  2-3.  G.  =  1.99.  Vitreous  lus- 
ter. Colorless,  white,  gray.  Fusible  at  1.5,  giving  yellow  flame 
of  sodium.  Gives  alkaline  reaction  after  ignition.  Effervesces  in 
acids.  Concentrated  hydrochloric  acid  solution  gives  precipitate  of 
calcium  sulphate  with  sulphuric  acid.  A  rare  species,  found  in  salt- 
lake  deposits  at  Merida,  Venezuela,  and  near  Ragtown,  Nevada. 

Other  rarer  species  in  this  division  include  hydrozincite, 
ZnC03.2Zn(OH)2;  trona,  Na2C03.HNaC03.2H20;  hydromag- 
nesite,  3MgC03.Mg(OH)2.3H20. 

SILICATES. 

The  silicates  form  the  largest  single  section  of  the  Chemical 
Classification  of  Minerals.  They  may  be  divided  into  (1)  An- 
hydrous Silicates,  (2)  Hydrous  Silicates. 

ANHYDROUS  SILICATES. 

This  section  may  be  subdivided  into  (1)  Disilicates,  Poly  sili- 
cates, being  salts  of  di silicic  acid,  H2Si206,  or  polysilicic  acid, 
H4Si308;  (2)  Metasilicates,  being  salts  of  metasilicic  acid,  H2Si03; 
(3)  Orthosilicates,  being  salts  of  orthosilicic  acid,  H4Si04;  (4)  Sub- 
silicates,  including  various  basic  species. 

1.    DISILICATES,   POLYSILICATES. 

The  only  representative  of  the  disilicates  of  sufficient  impor- 
tance to  warrant  mention  here  is  the  rare  lithium  mineral,  petal- 
ite,  LiAl(Si206)2. 

THE   FELDSPAR   GROUP. 

The  feldspars  form  one  of  the  most  important  of  mineral 
groups.  They  are  polysilicates  of  aluminium  with  either  potas- 
sium, sodium  and  calcium  and  rarely  barium.  They  may  belong 
to  either  the  monoclinic  or  the  triclinic  systems  but  with  the 
crystals  of  the  different  species  resembling  each  other  closely  in 
angles,  habits  of  crystallization,  and  methods  of  twinning.  They 
all  show  cleavages  in  two.  directions  which  make  an  angle  of  90°, 
or  closely  90°,  with  each  other.  Hardness  is  about  6  and  spe- 
cific gravity  2.6. 


ORTHOCLASE 


221 


MONOCLINIC   SECTION. 

Orthoclase.     Potash  Feldspar. 

Composition.  Potassium-aluminium  silicate,  KAlSi308  = 
Silica  64.7,  alumina  18.4,  potash  16.9.  Soda  sometimes  re- 
places a  portion  of  the  potash. 

Crystallization.  Monoclinic.  Crystals  are  usually  prismatic 
in  habit  and  have  as  prominent  forms;  clinopinacoid,  base,  prism, 
with  often  smaller  orthodomes  (Figs.  288,  289  and  290).  Fre- 


m 


Fig.  289. 


Fig.  288. 


Fig.  290. 


quently  twinned;  Carlsbad  with  clinopinacoid  as  twinning  plane 
(Fig.  291);  Baveno  with  clinodome  as  twinning  plane  (Fig.  292); 
Manebach  with  base  as  twinning  plane  (Fig.  293). 


Fig.  291. 
Carlsbad  Twin. 


Fig.  292. 
Baveno  Twin. 


Fig.  293. 
Manebach  Twin. 


Structure.   Usually  crystallized  or  coarsely  cleavable  to  granu- 
lar;  more  rarely  fine-grained,  massive  and  cryptocrystalline. 


222  MANUAL  OF  MINERALOGY 

Physical  Properties.  Two  prominent  cleavages  (one  parallel 
to  base,  perfect:  the  other  parallel  to  clinopinacoid,  good),  mak- 
ing an  angle  of  90°  with  each  other.  H.  =  6-6.5.  G.  =  2.5-2.6. 
Luster  vitreous.  Colorless,  white,  gray,  flesh-red,  more  rarely 
green.  Streak  white. 

Varieties.  Common  feldspar  is  the  usual  opaque  variety. 
Adularia  is  white  or  colorless  and  translucent  to  transparent. 
Some  adularia  shows  an  opalescent  play  of  colors,  and  is  called 
moonstone.  Most  of  the  moonstones,  however,  belong  to  the 
members  of  the  plagioclase  feldspar  series.  Sanidine,  or  glassy 
feldspar,  is  a  variety  occurring  in  glassy,  often  transparent, 
phenocrysts  in  eruptive  rocks. 

Tests.  Difficultly  fusible  (5).  Insoluble  in  acids.  When 
mixed  with  powdered  gypsum  and  heated  on  platinum  wire  gives 
the  violet  flame  of  potassium.  Usually  to  be  recognized  by  its 
color,  hardness  and  cleavage.  Distinguished  from  the  other 
feldspars  by  its  right-angle  cleavage  and  the  lack  of  striations 
on  the  best  cleavage  surface. 

Alteration.  When  acted  upon  by  waters  carrying  carbon 
dioxide  in  solution,  orthoclase  alters,  forming  a  soluble  carbonate 
of  potassium  and  leaving  as  a  residue  either  a  mixture  of  kaolin 
(H4Al2Si209)  and  quartz  (Si02),  or  of  muscovite  (H2K(AlSi04)3) 
and  quartz.  Kaolin  forms  the  chief  constituent  of  clays  and 
has  been  derived  in  this  manner. 

Occurrence.  One  of  the  most  common  of  minerals.  Widely  dis- 
tributed as  a  prominent  rock  constituent,  occurring  in  all  types  of 
rocks;  igneous,  in  granites,  syenites,  porphyries,  etc.;  sedimentary, 
in  certain  sandstones  and  conglomerates;  metamorphic,  in  gneisses. 
Also  in  large  crystals  and  cleavable  masses  in  pegmatite  veins,  asso- 
ciated chiefly  with  quartz,  muscovite  and  albite.  These  veins  are 
to  be  found  where  granite  rocks  abound.  Large  veins  of  this  char- 
acter from  which  feldspar  is  quarried  in  considerable  amounts  occur 
in  the  New  England  and  Middle  Atlantic  states,  chiefly  in  Maine, 
Connecticut,  New  York,  Pennsylvania  and  Maryland. 

Name.  The  name  orthoclase  refers  to  the  right-angle  cleavage 
possessed  by  the  mineral.  Feldspar  is  derived  from  the  German 
word  j 'eld,  field. 


MICROCLINE  223 

Use.  Orthoclase  is  chiefly  used  in  the  manufacture  of  porce- 
lain. It  is  ground  very  fine  and  mixed  with  kaolin,  or  clay,  and 
quartz.  When  heated  to  high  temperature  the  feldspar  fuses 
and  acts  as  a  cement  to  bind  the  material  together.  Fused 
feldspar  also  furnishes  the  major  part  of  the  glaze  on  porcelain 
ware. 

A  rare  barium  feldspar,  hyalophane  (K2,Ba)Al2Si40w,  belongs 
here. 

TRICLINIC    SECTION. 

Microcline. 

Composition.  Like  orthoclase,  KAlSi308  =  Silica  64.7,  alu- 
mina 18.4,  potash  16.9. 

Crystallization.  Triclinic.  Axial  lengths  and  angles  only 
slightly  different  from  those  of  orthoclase.  Ordinarily  the  crys- 
tals of  the  two  species  cannot  be  told  apart  except  by  very 
accurate  measurements  or  a  microscopical  examination.  Micro- 
cline crystals  are  usually  twinned  according  to  the  same  laws 
as  orthoclase.  Also  microscopically  twinned  according  to  the 
albite  and  pericline  laws,  characteristic  of  the  triclinic  feldspars. 
A  thin  section  of  microcline  under  the  microscope  in  polarized 
light  usually  shows  a  characteristic  grating  structure,  caused  by 
the  crossing  at  nearly  right  angles  of  the  twin  lamellae  formed 
according  to  these  triclinic  twinning  laws.  Orthoclase,  being 
monoclinic,  could  not  show  such  twinning. 

Structure.     In  cleavable  masses  or  in  crystals. 

Physical  Properties.  Cleavage  parallel  to  base  and  brachy- 
pinacoid,  with  angle  of  89°  30'  (orthoclase  would  have  90°). 
H.  =  6-6.5.  G.  =  2.54-2.57.  Vitreous  luster.  Color  white 
to  pale  yellow.  Also  sometimes  green  (Amazon  stone)  or  red. 
Transparent  to  translucent. 

Tests.  Same  as  for  orthoclase.  The  two  species  only  to  be 
distinguished  from  each  other  by  careful  examination  (see  above) . 

Occurrence.  Same  as  for  orthoclase.  Much  that  passes  as  ortho- 
clase in  reality  is  microcline.  Occurs  with  a  green  color  in  the  Ural 
Mts.  and  at  Pike's  Peak,  Colorado,  and  is  known  as  Amazon  stone. 


224  MANUAL  OF  MINERALOGY 

Name.  Microcline  is  derived  from  two  Greek  words  meaning 
little  and  inclined,  referring  to  the  slight  variation  of  the  cleavage 
angle  from  90°. 

Use.  Same  as  for  orthoclase.  Amazon  stone  is  at  times 
polished  and  used  as  an  ornamental  material. 

THE    PLAGIOCLASE    FELDSPARS.     ALBITE-ANORTHITE 

SERIES. 

The  triclinic  soda-lime  feldspars  embrace  a  series  of  isomor- 
phous  minerals  varying  in  composition  from  albite,  NaAlSi308,  to 
anorthite,  CaAl2Si208.  These  two  molecules  can  replace  each 
other  in  any  proportion,  and  as  a  consequence  a  practically  com- 
plete series  may  be  found  from  the  pure  soda  feldspar,  and  then 
with  gradually  increasing  amounts  of  the  anorthite  molecule, 
to  the  pure  lime  feldspar.  Definite  names  have  been  given  to 
various  mixtures  of  these  two  molecules,  the  more  important 
being  listed  below: 

Albite,          NaAlSi308. 

Oligoclase,    3NaAlSi308.lCaAl2Si208. 

Andesine,      lNaAlSi308.lCaAl2Si208. 

Labradorite,  lNaAlSi308.3CaAl2Si208. 

Anorthite,      CaAl2Si208. 

These  triclinic  feldspars  crystallize  in  forms  closely  resembling 
those  of  the  monoclinic  orthoclase,  and  the  axial  lengths  and  in- 
clinations are  also  closely  the  same.  This  similarity  in  the  crys- 
tal structure  between  the  monoclinic  and  triclinic  feldspars  is 
best  shown  by  a  comparison  of  the  cleavage  angles  of  the  different 
species,  that  of  orthoclase  being  90°,  of  albite  86°  24',  and  of 
anorthite  85°  50'.  The  triclinic  feldspars  are  often  known  as 
the  plagioclase  feldspars,  because  of  their  oblique  cleavage. 

The  crystals  of  the  plagioclase  feldspars  are  frequently  twinned 
according  to  the  various  laws  governing  the  twins  of  orthoclase, 
i.e.,  the  Carlsbad,  Baveno  and  Manebach  laws.  They  are  also 
practically  always  twinned  according  to  one  or  both  of  two  laws, 
known  as  the  albite  and  pericline  laws.  The  twinning  plane 
in  the  albite  law  is  the  brachypinacoid,  which  corresponds  to 
the  clinopinacoid  in  orthoclase.  The  angle  between  the  basal 


ALBITE 


225 


plane  and  this  twinning  plane  is  not  90°,  but  about  86°;  so  that 
if  one  imagines  a  triclinic  feldspar  crystal  cut  in  two  along  this 
plane  and  one-half  revolved  180°  from  its  original  position 
upon  an  axis  perpendicular  to  the  plane,  there  would  then  be 
formed  a  shallow  trough  along  the  upper  surface  of  the  crys- 
tal, because  the  basal  planes  of  the  two  adjacent  halves  would 
not  lie  in  the  same  plane,  but  rather  slope  at  a  slight  angle 
toward  each  other.  This  sort  of  twinning  is  commonly  repeated 
many  times  in  a  single  crystal,  and  gives  rise  to  thin  lamellae,  each 
one  in  twin  position  in  respect  to  those  on  either  side  (see  Figs. 
296  and  297).  Consequently  a  basal  plane  or  cleavage  surface 
of  such  a  twinned  crystal  will  be  crossed  by  a  number  of  parallel 
groovings  or  striations  (Fig.  298).  Many  times  these  striations 
are  so  fine  as  not  to  be  visible  to  the  unaided  eye,  but  also  at 
times  they  are  coarse  and  easily  seen.  The  presence  of  these 
striation  lines  upon  the  better  cleavage  surface  of  a  feldspar  is 
one  of  the  best  proofs  that  it  belongs  to  the  plagioclase  series. 
In  the  pericline  law  the  twinning  axis  is  the  b  crystallographic 
axis,  and  when  this  results  in  polysynthetic  twins  the  consequent 
striations  are  to  be  seen  on  the  brachypinacoid. 

Albite.     Soda-feldspar. 

Composition.  Sodium-aluminium  silicate,  NaAlSi308=  Silica 
68.7,  alumina  19.5,  soda  11.8.  Calcium  is  usually  present  in 
small  amount  in  the  form  of  the  anorthite  molecule,  CaAl2Si208. 

Crystallization.    Triclinic.    Usually  in  tabular  crystals  paral- 


Fig.  294.  Fig.  295.  Fig.  296.    Albite  Twin. 

lei  to  brachypinacoid  (Fig.  294).    Sometimes  elongated  parallel 
to  6  crystal  axis  (Fig.  295).    Twinning  very  common,  according 


226  MANUAL  OF  MINERALOGY 

to  the  albite  law  (see  above)  and  evidenced  by  fine  striation  lines 
on  the  better  cleavage  surface  (Figs.  297  and  298).  Twinning 
according  to  the  other  laws  frequent. 


Fig.  297.  Fig.  298.    Albite  Twinning. 

Structure.  Commonly  massive,  either  lamellar  with  lamellae 
often  curved  or  in  cleavable  masses.  Distinct  crystals  rare. 

Physical  Properties.  Perfect  cleavage  parallel  to  base;  good 
cleavage  parallel  to  brachypinacoid.  Cleavage  angle  86°  24'. 
H.=  6.  G.=  2.62.  Vitreous  luster;  sometimes  pearly  on  cleav- 
age surface.  Colorless,  white,  gray.  Transparent  to  opaque. 

Tests.  Fusible  at  4-4.5,  giving  yellow  flame  (sodium).  In- 
soluble in  acids.  Characterized  by  its  hardness,  white  color, 
cleavage,  frequently  curved  lamellar  structure,  striations  on 
better  cleavage  .surface,  etc. 

Occurrence.  Like  orthoclase,  a  widely  distributed  and  important 
rock-making  mineral.  It  occurs  in  all  classes  of  rocks,  but  particu- 
larly in  those  of  igneous  origin,  such  as  granites,  syenites,  porphy- 
ries arid  felsite  lavas.  Found  commonly,  also,  in  pegmatite  veins. 
Notable  localities  for  albite  are  to  be  found  in  Switzerland  and  the 
Tyrol;  in  the  United  States  at  Paris,  Maine;  Chesterfield,  Mas- 
sachusetts; Haddam  and  Branch ville,  Connecticut;  Amelia  Court 
House,  Virginia,  etc. 

Name.     From  the  Latin  albus,  white,  in  allusion  to  its  color. 

Use.  Has  the  same  uses  as  orthoclase,  but  not  so  commonly 
employed.  Some  varieties,  when  polished,  show  an  opalescent 
play  of  colors  and  are  known  as  moonstones.  Other  members 


OLIGOCLASE  227 

of  the  plagioclase  series  and  orthoclase  show  at  times  this  same 
effect.  The  stones  are  usually  cut  in  round  or  oval  shapes  and 
are  valued  up  to  $3  a  carat.  The  finest  moonstones  come  from 
Ceylon,  but  they  are  chiefly  orthoclase. 

Oligoclase. 

Composition.  Intermediate  between  albite  and  anorthite, 
chiefly  near  3NaAlSi308.lCaAl2Si208. 

Crystallization.     Triclinic.     Like  albite. 

Structure.  Usually  massive,  cleavable  to  compact.  Crystals 
rare. 

Physical  Properties.  Cleavage  in  two  directions  at  86°  32'. 
One  cleavage  (parallel  to  base)  is  better  than  the  other,  and  on 
this  parallel  striation  lines  due  to  twinning  are  commonly  to  be 
seen.  H.  =  6.  G.  =  2.66.  Vitreous  to  pearly  luster.  Color  usu- 
ally whitish  with  faint  tinge  of  grayish  green,  also  reddish  white, 
etc.  Translucent  to  opaque. 

Tests.  Fusible  at  4-4.5.  Insoluble  in  hydrochloric  acid. 
To  be  told  from  albite  only  by  a  test  for  calcium.  Briefly,  the 
test  is  made  as  follows:  Fuse  powdered  mineral  with  sodium 
carbonate;  dissolve  fusion  in  hydrochloric  acid  and  evaporate 
to  dryness,  moisten  residue  with  water  and  a  little  nitric  acid, 
boil  and  then  filter  off  insoluble  silica;  to  filtrate  add  ammonium 
hydroxide  in  excess,  filter  off  precipitate  of  aluminium  hydrox- 
ide; in  filtrate  get  precipitate  of  calcium  oxalate  upon  addition 
of  ammonium  oxalate.  To  be  positively  distinguished  from  an- 
desine  and  labradorite  only  by  a  chemical  analysis  or  an  optical 
examination. 

Occurrence.  Like  albite,  but  not  so  common.  Found  in  various 
localities  in  Norway,  notably  at  Tvedestrand,  where  it  contains  in- 
clusions of  hematite,  which  give  the  mineral  a  golden  shimmer  and 
sparkle.  Such  feldspar  is  called  aventurine  oligoclase,  or  sunstone. 
Occurs  in  the  United  States  at  Fine  and  Macomb,  St.  Lawrence 
County,  New  York;  Danbury  and  Haddam,  Connecticut;  Bakers- 
ville,  North  Carolina,  etc. 

Name.  Derived  from  two  Greek  words  meaning  little  and 
fracture. 


228  MANUAL  OF  MINERALOGY 

Use.  Occasionally  used  as  an  ornamental  material,  in  the 
varieties  sunstone  and  moonstone. 

Andesine. 

Composition.  Intermediate  between  albite  and  anorthite, 
corresponding  chiefly  to  lNaAlSi308.lCaAl2Si208. 

Crystallization.     Triclinic.    Like  albite. 

Structure.     In  cleavable  masses.     Crystals  rare. 

Physical  Properties.  Cleavage  in  two  directions  at  86°  14'. 
One  cleavage  (parallel  to  base)  better  than  the  other,  and  on  this 
parallel  striation  lines  due  to  twinning  are  commonly  to  be  seen. 
H.  =  6.  G.=  2.69.  Vitreous  to  pearly  luster.  Color  white, 
gray,  greenish,  yellowish,  flesh-red.  Often  exhibits  a  beautiful 
play  of  colors,  due  partly  to  the  intimate  twinning  and  partly  to 
inclusions. 

Tests.  Same  as  for  oligoclase.  To  be  positively  distinguished 
from  oligoclase  and  labradorite  only  by  a  chemical  analysis  or 
an  optical  examination. 

Occurrence.  Same  as  for  albite,  but  less  common.  More  fre- 
quently found  in  somewhat  more  basic  igneous  rocks,  i.e.,  those 
containing  less  silica  and  more  lime  and  magnesia. 

Name.  Occurs  in  a  rock  called  andesite,  found  in  the  Andes 
Mountains. 

Labradorite. 

Composition.  Intermediate  between  albite  and  anorthite, 
corresponding  chiefly  to  lNaAlSi308.3CaAl2Si208. 

Crystallization.     Triclinic.     Like  albite. 

Structure.     In  cleavable  masses.     Crystals  rare. 

Physical  Properties.  Cleavage  in  two  directions  at  86°  5'. 
One  cleavage  (parallel  to  base)  better  than  the  other,  and  on  this 
parallel  striation  lines  due  to  twinning  are  commonly"  shown. 
H.  =  6.  G.  =  2.73.  Vitreous  luster.  Usually  gray,  brown  or 
greenish;  sometimes  colorless  or  white.  Often  shows  a  beautiful 
play  of  colors,  due  in  part  to  the  intimate  twinning  structure, 
in  part  to  inclusions.  Transparent  to  ODaque. 

Tests.    Same  as  for  oligoclase. 


LEUCITE  229 

Occurrence.  Like  albite,  but  more  commonly  in  the  darker 
colored  basic  igneous  rocks,  and  usually  associated  with  pyroxene 
or  amphibole.  Found  on  the  coast  of  Labrador  in  large  amounts, 
associated  with  hypersthene  and  magnetite,  and  when  polished 
showing  a  fine  iridescent  play  of  colors. 

Use.    As  an  ornamental  stone. 

Anorthite. 

Composition.  Calcium-aluminium  silicate,  CaAl2Si208  =  Silica 
43.2,  alumina  36.7,  lime  20.1.  Soda  is  usually  present,  in  small 
amount,  in  the  albite  molecule,  NaAlSi308. 

Crystallization.  Triclinic.  Crystals  usually  prismatic  paral- 
lel to  vertical  axis.  Twinning  common  according  to  albite  and 
pericline  laws  (see  above).  . 

Structure.     Massive  cleavable.     Crystals  rare. 

Physical  Properties.  Cleavage  in  two  directions  at  85°  50'. 
One  cleavage  (parallel  to  base)  better  than  the  other.  H.=  6. 
G.  =  2.75.  Vitreous  to  pearly  luster.  Color  white,  grayish, 
reddish.  Transparent  to  opaque. 

Tests.  Fusible  at  4.5.  Dissolves  slowly  in  hydrochloric  acid 
and  yields  a  silica  jelly  upon  evaporation.  Gives  a  strong  test 
for  calcium  (see  under  oligoclase)  and  only  a  slight  yellow  flame 
(sodium). 

Occurrence.  A  rock-making  mineral,  particularly  in  the  dark- 
colored  basic  igneous  rocks.  Associated  with  various  calcium  and 
magnesium  silicates.  Found  in  the  lavas  of  Mount  Vesuvius;  of 
Japan,  etc. 

Name.  Derived  from  the  Greek  word  meaning  oblique,  be- 
cause of  its  triclinic  crystallization. 

2.    METASILICATES. 
Leucite. 

Composition.  A  metasilicate  of  aluminium  and  potassium, 
KAl(Si03)2  =  Silica  55.0,  alumina  23.5,  potash  21.5. 

Crystallization.  Isometric.  Trapezohedral  habit  (Fig.  299). 
Other  forms  rare.  Strictly  isometric  only  at  temperatures  of 


230  MANUAL  OF  MINERALOGY 

500°  C.  or  over.  On  cooling  below  this  temperature  it  under- 
goes an  internal  molecular  rearrangement  to  that  of  some  other 
crystal  system,  but  the  external  form  does 
not.  change.  It  is  formed  in  lavas  at 
high  temperatures  and  is  then  isometric 
in  internal  structure  as  well  as  outward 
form. 

Structure.     Usually  in  distinct  crys- 
tals, also  in  disseminated  grains. 

Physical     Properties.        H.  =  5.5-6. 
Fi    299  G.  =  2.5.    Vitreous  to  dull  luster.    Color 

white  to  gray.  Translucent  to  opaque. 
Tests.  Infusible.  Decomposed  by  hydrochloric  acid  with 
the  separation  of  silica  but  without  the  formation  of  a  jelly. 
Addition  of  ammonia  to  the  solution  gives  precipitate  of  alu- 
minium hydroxide.  When  mixed  with  powdered  gypsum  and 
fused  gives  violet  potassium  flame  (best  observed  through  a 
blue  glass). 

Occurrence.  A  rather  rare  mineral,  occurring  almost  wholly  in 
lavas.  Found  in  rocks  in  which  the  amount  of  potassium  in  the 
magma  was  in  excess  of  the  amount  necessary  to  form  feldspar.  Is 
not  observed,  therefore,  in  rocks  that  show  quartz.  Chiefly  found 
in  the  rocks  of  central  Italy;  notably  as  phenocrysts  in  the  lavas 
of  Vesuvius.  Pseudomorphs  after  leucite  are  found  in  syenites  of 
Arkansas,  Montana,  Brazil,  etc. 

Name.     From  a  Greek  word  meaning  white. 

Pollucite,  H2Cs2Al2(Si03)6,  is  a  rare  mineral  that  belongs  in  the 
same  group  as  leucite. 

PYROXENE   GROUP. 

The  Pyroxene  Group  includes  a  series  of  related  metasilicates 
which  have  calcium,  magnesium  and  ferrous  iron  as  the  im- 
portant bases,  also  manganese  and  zinc.  Further  certain  mole- 
cules contain  the  alkalies  and  aluminium  and  ferric  iron.  They 
may  belong  to  either  the  orthorhombic,  monoclinic  or  triclinic 
systems,  but  the  crystals  of  the  different  species  are  closely 
similar  in  many  respects. 


PYROXENE  281 

ORTHORHOMBIC   SECTION. 
Enstatite,  Bronzite,  Hypersthene. 

A  group  of  orthorhombic  members  of  the  pyroxene  group,  en- 
statite  being  magnesium  metasilicate,  MgSiO3;  bronzite,  the  same  as 
enstatite,  with  small  amounts  of  iron  replacing  the  magnesium; 
hypersthene,  an  iron-magnesium  metasilicate,  (Mg,Fe)SiOs.  Dis- 
tinct crystals  rare.  Usually  foliated  massive  with  good  cleavage; 
fibrous,  etc.  Color  from  white  in  enstatite  to  green  and  brown  with 
increase  in  iron.  Rock-making  minerals,  occurring  like  the  mono- 
clinic  pyroxenes  but  much  rarer.  Found  in  basic  igneous  rocks, 
such  as  peridotite,  gabbro,  etc. 

Pyroxene. 

Composition.  Pyroxene  is  a  metasilicate,  varying  in  its  com- 
position. It  contains  as  bases  chiefly  calcium  and  magnesium, 
with  smaller  amounts  of  ferrous  iron.  In  some  varieties,  how- 
ever, molecules  are  introduced  in  which  are  the  alkalies  (chiefly 
sodium),  aluminium  and  ferric  iron.  The  more  important  varie- 
ties of  pyroxene  with  the  formulas  assigned  to  them  follow. 

Diopside,  CaMg(Si03)2. 

Common  pyroxene,  Ca(Mg,Fe)(Si03)2. 

Augite,  CaMg(Si03)2  with  MgAl2Si06  and  NaAlSi206;  with 
iron  isomorphous  with  both  the  magnesium  and  the  alu- 
minium. 

These  varieties  form  an  isomorphous  series,  and  all  gradations 
between  them  appear.  Other  varieties  of  less  common  occur- 
rence are  hedenbergite,  CaFe(Si03)2;  schefferite,  a  manganese 
pyroxene;  jeffersonite,  a  manganese-zinc  pyroxene. 

Crystallization.  Monoclinic.  Crystals  prismatic  in  habit; 
prism  faces  make  angles  of  87°  and  93°  with  each  other.  The 
prism  zone  commonly  shows  the  prism  faces  truncated  by  the 
faces  of  both  vertical  pinacoids,  so  that  the  crystals  show,  when 
viewed  parallel  to  the  vertical  axis,  a  rectangular  cross  section 
with  truncated  corners.  The  interfacial  angles  in  the  prism 
zone  are  either  exactly  or  very  closely  90°  and  45°.  The  ter- 
minations vary,  being  made  up  frequently  of  a  combination  of 


232 


MANUAL  OF  MINERALOGY 


the  basal  plane  with  pyramids  both  in  front  and  behind  (Figs. 
300-302). 


Fig.  300. 


Fig.  301. 


Fig.  302. 


Structure.  In  crystals.  Often  lamellar.  Coarse  to  fine  gran- 
ular. 

Physical  Properties.  Prismatic  cleavage  sometimes  good, 
often  interrupted.  Sometimes  basal  parting  observed,  often 
shown  by  twinning  lamellae  (see  Fig.  A,  pi.  X).  H.  =  5-6. 
G.=  3.2-3.6.  Vitreous  luster.  Color  varying  from  white  and 
light  green  in  diopside,  to  green  in  pyroxene,  through  dark  green 
to  black  in  augite.  Color  deepens  with  increase  in  the  amount 
of  iron  present.  Transparent  to  opaque. 

Tests.  Fusible  from  4  to  4.5.  Insoluble  in  hydrochloric  acid. 
To  test  for  bases :  fuse  with  sodium  carbonate ;  dissolve  in  nitric 
acid;  evaporate  to  dryness;  notice  the  formation  of  silica  jelly; 
moisten  residue  with  water  and  hydrochloric  acid;  boil  and 
filter  from  insoluble  silica;  add  ammonium  hydroxide  in  excess, 
precipitate  of  aluminium  and  ferric  hydroxide;  to  boiling  filtrate 
add  ammonium  oxalate,  precipitate  of  calcium  oxalate;  to  filtrate 
add  sodium  phosphate,  precipitate  of  ammonium  magnesium 
phosphate.  Recognized  usually  by  its  characteristic  crystals. 

Occurrence.  The  pyroxenes  are  common  and  important  rock- 
making  minerals,  being  found  chiefly  in  the  dark  colored  igneous 
rocks,  especially  those  whose  magmas  were  rich  in  iron,  calcium  and 
magnesium.  They  are  seldom  to  be  found  in  rocks  that  contain 
much  quartz.  Augite  is  found  in  basaltic  lavas,  and  in  the  dark 


PLATE  X. 


A.    Pyroxene  showing  Twinning  Lamellae  due  to  Basal  Parting. 
B     Spodumene  Crystal  from  Huntington,  Massachusetts. 
C      Garnet  Crystals  in  Mica-Schist. 


SPODUMENE  233 

colored  intrusions  known  generally  as  trap,  in  gabbros  and  perido- 
tites.  Diopside  and  common  pyroxene  are  found  sometimes  in 
syenites  and  similar  rocks;  also  as  metamorphic  minerals  in  impure 
recrystallized  dolomitic  limestones.  Common  pyroxene  also  occurs 
in  some  gneisses.  In  the  limestones,  pyroxene  is  often  associated 
with  tremolite,  scapolite,  vesuvianite,  garnet,  titanite,  phlogopite, 
etc.  In  igneous  rocks  it  is  found  with  orthoclase,  the  plagioclase 
feldspars,  nephelite,  chrysolite,  leucite,  amphibole,  magnetite,  etc. 
Some  of  the  notable  localities,  particularly  for  fine  crystals,  are  the 
following:  For  diopside.  Ala,  Piedmont;  Traversella;  Nordmark, 
Sweden;  in  various  localities  in  Orange  County,  New  York;  for 
augite,  in  the  lavas  of  Vesuvius ;  at  Fassathal,  Tyrol ;  Bilin,  Bohemia ; 
hedenbergite  from  Sweden  and  Norway;  schefferite  from  Sweden; 
jeffersonite  from  Franklin,  New  Jersey. 

Names.  The  name  pyroxene,  stranger  to  fire,  is  a  misnomer, 
and  was  given  to  the  mineral  because  it  was  thought  that  it  did 
not  occur  in  igneous  rocks.  Diopside  comes  from  two  Greek 
words  meaning  double  appearance.  Augite  comes  from  a  Greek 
word  meaning  luster. 

Use.  Clear  green  diopside  or  common  pyroxene  is  occasion- 
ally used  as  a  gem  material. 

^Egirite  or  Acmite. 

A  soda-ferric  iron  pyroxene,  NaFe"'(SiO3)2.  Monoclinic.  Slender 
prismatic  crystals,  often  with  steep  terminations.  Faces  often  im- 
perfect. Imperfect  prismatic  cleavage  with  93°  angle.  H.  =  6-6.5. 
G.  =  3.5-3.55.  Vitreous  luster.  Color  brown  or  green.  Trans- 
lucent to  opaque.  Fusible  at  3.5,  giving  yellow  sodium  flame. 
Fused  globule  slightly  magnetic.  A  comparatively  rare  rock-mak- 
ing mineral  found  chiefly  in  nephelite-syenite  and  phonolite. 

Spodumene. 

Composition.  Lithium-aluminium  metasilicate,  LiAl(SiOs)2  = 
Silica  64.5,  alumina  27.4,  lithia  8.4.  Usually  has  a  small  amount 
of  sodium  replacing  the  lithium. 

Crystallization.  Monoclinic.  Prismatic  crystals,  flattened 
frequently  parallel  to  the  orthopinacoid.  Deeply  striated  ver- 
tically (see  Fig.  B,  pi.  X).  Crystals  usually  coarse  and  with 
roughened  faces.  Sometimes  very  large. 

Structure.     In  crystals  or  cleavable  masses. 


234  MANUAL  OF  MINERALOGY 

Physical  Properties.  Perfect  prismatic  cleavage.  H.  =  6.5- 
7.  G.  =  3.18.  Vitreous  luster.  Color  white,  gray,  pink,  yel- 
low, green.  Transparent  to  translucent  when  unaltered. 

Tests.  Fusible  at  3.5,  throwing  out  fine  branches  at  first,  and 
then  fusing  to  a  clear  glass.  Gives  a  crimson  flame  (lithium). 
Insoluble  in  acids. 

Varieties.  Ordinary.  Color  white  or  gray,  sometimes  pink. 
Commonly  in  flattened  prismatic  crystals,  often  very  large. 
Frequently  altered  to  other  minerals. 

Hiddenite.  A  clear,  transparent  variety  ranging  in  color  from 
yellow-green  to  deep  emerald.  Found  in  small  striated  and 
etched  crystals. 

Kunzite.  A  transparent  variety  ranging  from  pale  pink  to 
deep  amethystine  purple.  Has  been  found  in  flattened  crystals 
8  to  10  inches  in  length,  5  to  6  in  breadth. 

Alteration.  Spodumene  very  easily  alters  to  other  species, 
becoming  dull  and  opaque.  The  alteration  products  include 
albite,  eucryptite  (LiAlSi04),  muscovite,  microcline. 

Occurrence.  A  comparatively  rare  species,  but  found  occasion- 
ally in  very  large  crystals  in  pegmatite  veins.  Occurs  at  Goshen, 
Chesterfield,  Chester,  Huntington  and  Sterling,  Massachusetts; 
Branchville,  Connecticut;  Etta  tin  mine,  Pennington  County,  South 
Dakota,  in  crystals  measuring  many  feet  in  length.  Hiddenite 
occurs  with  emerald  beryl  at  Stony  Point,  Alexander  County, 
North  Carolina.  Kunzite  is  found  with  pink  beryl  in  San  Diego 
County,  California. 

Names.  Spodumene  comes  from  a  Greek  word  meaning  ash 
colored.  Hiddenite  is  named  for  Mr.  W.  E.  Hidden;  kunzite  for 
Dr.  G.  F.  Kunz.  ) 

Use.  The  varieties  hiddenite  and  kunzite  furnish  very  beauti- 
ful gem  stones  but  are  limited  in  their  occurrence. 

Jadeite. 

A  sodium-aluminium  metasilicate,  NaAl(SiO3)2.  Massive,  gran- 
ular to  closely  compact.  H.  =  6.5-7.  G.  =  3.33-3.35.  Vitreous 
luster.  Color  white,  gray  to  light  green.  Translucent  to  opaque. 
Very  tough.  Fuses  at  2.5,  coloring  the  flame  yellow  (sodium). 
Forms  in  part  the  material  known  as  jade  and  highly  prized  by 
oriental  peoples  as  an  ornamental  material.  Made  into  finely  carved 


PECTOLITE  235 

ornaments  and  utensils,  and  when  of  fine  color  and  translucent  com- 
mands a  high  price.  Found  chiefly  in  Upper  Burmah,  in  southern 
China  and  in  Thibet. 

Wollastonite. 

Composition.  Calcium  metasilicate,  CaSi03  =  Silica  51.7, 
lime  48.3. 

Crystallization.  Monoclinic.  Usually  in  tabular  crystals, 
with  either  base  or  orthopinacoid  prominent. 

Structure.  Commonly  massive,  cleavable  to  fibrous;  also 
compact. 

Physical  Properties.  Perfect  cleavage  parallel  to  orthopina- 
coid. H.  =  5-5.5.  G.  =  2.8-2.9.  Vitreous  luster,  pearly  on 
cleavage  surfaces.  Sometimes  silky  when  fibrous.  Colorless, 
white  or  gray.  Translucent  to  opaque. 

Tests.  Fusible  at  4  to  a  white,  almost  glassy  globule.  De- 
composed by  hydrochloric  acid,  with  the  separation  of  silica  but 
without  the  formation  of  a  jelly.  Filtered  solution  with  ammo- 
nium hydroxide  and  ammonium  carbonate  gives  white  precipi- 
tate of  calcium  carbonate. 

Occurrence.  Commonly  found  in  crystalline  limestones  which 
have  been  metamorphosed  either  through  the  heat  and  pressure 
attendant  upon  the  intrusion  into  them  of  igneous  rocks  or  upon 
movements  of  the  earth's  crust.  An  impure  limestone,  containing 
quartz  for  instance,  under  these  conditions  will  become  crystalline, 
and  new  minerals,  such  as  wollastonite,  be  formed.  Associated  with 
calcite,  diopside,  lime  garnet,  tremolite,  lime  feldspars,  vesuvianite, 
epidote,  etc.  May  at  times  be  so  plentiful  as  to  constitute  the  chief 
mineral  of  the  rock  mass.  Such  wollastonite  rocks  are  found  in 
California,  the  Black  Forest,  Brittany,  etc.  More  rarely  found  in 
feldspathic  schists. 

Pectolite. 

Composition.  HNaCa2(Si03)3  =  Silica  54.1,  lime  33.8,  soda 
9.3,  water  2.7. 

Crystallization.  Monoclinic.  Crystals  usually  elongated 
parallel  to  the  ortho-axis. 

Structure.  Usually  in  aggregates  of  acicular  crystals.  Fre- 
quently radiating,  with  fibrous  appearance.  Sometimes  com- 
pact. 


236  MANUAL  OF  MINERALOGY 

Physical  Properties.  Perfect  cleavage  parallel  to  the  ortho- 
pinacoid.  H.  =  5.  G.  =  2.7-2.8.  Vitreous  to  pearly  luster. 
Colorless,  white  or  gray. 

Tests.  Fuses  quietly  at  2.5-3  to  a  glass;  colors  flame  yellow 
(sodium).  Decomposed  by  hydrochloric  acid,  with  the  separa- 
tion of  silica  but  without  the  formation  of  a  jelly.  Filtered  solu- 
tion with  ammonium  hydroxide  and  ammonium  carbonate  gives 
white  precipitate  of  calcium  carbonate.  Water  in  C.  T. 

Occurrence.  A  mineral  of  secondary  origin  similar  in  its  occur- 
rence to  the  zeolites.  Found  lining  amygdaloidal  cavities  in  basalt, 
associated  with  various  zeolites,  phrenite,  calcite,  etc.  Found  at 
Bergen  Hill  and  West  Paterson,  New  Jersey. 


TRICLINIC   SECTION. 
Rhodonite. 

Composition.    Manganese  metasilicate,  MnSi03  =  Silica  45.9, 
manganese  protoxide  54.1.    Iron,  calcium  and  sometimes  zinc 
replace  a  part  of  the  manganese. 

Crystallization.  Triclinic.  Crystals 
commonly  tabular  parallel  to  base  (Fig. 
303) .  Crystals  often  rough  with  rounded 


Structure.     Commonly  massive,  cleav- 
able  to  compact;  in  embedded  grains. 
Fig'  nice'  N?wajSyFur~        Physical  Properties.    Prismatic  cleav- 
age at  about  92°.    H.  =  6-6.5.   G.  =  3.63. 
Vitreous  luster.     Color  rose-red,  pink,  brown.   .Translucent  to 
opaque. 

Tests.  Fusible  (3-3.5)  to  a  nearly  black  glass.  Insoluble  in 
hydrochloric  acid.  In  0.  F.  gives  clear  reddish  violet  color  to 
borax  bead. 

Occurrence.  Found  at  Langban,  Sweden,  with  iron  ore;  found 
in  large  masses  near  Ekaterinburg,  Urals;  from  Broken  Hill,  New 
South  Wales.  A  zinciferous  variety,  known  as  foivlerite,  occurs  in 
good-sized  crystals  in  limestone  with  franklinite,  willemite,  zincite, 
etc.,  at  Franklin  Furnace,  New  Jersey. 


AMPHIBOLE  237 

Name.  Derived  from  the  Greek  word  for  a  rose,  in  allusion 
to  the  color. 

Use.  Sometimes  polished  for  use  as  an  ornamental  stone. 
Obtained  chiefly  from  the  Urals. 

AMPHIBOLE   GROUP. 

The  minerals  of  the  Amphibole  Group  crystallize  in  either  the 
orthorhombic,  monoclinic  or  triclinic  systems,  but  the  crystals 
of  the  different  species  are  closely  similar  in  many  respects. 
Chemically  they  form  a  series  parallel  to  that  of  the  Pyroxene 
Group  (page  230),  being  metasilicates  with  calcium,  magnesium 
and  ferrous  iron  as  important  bases,  and  also  with  manganese 
and  the  alkalies.  Certain  molecules  that  are  present  in  some 
varieties  contain  aluminium  and  ferric  iron. 

ORTHORHOMBIC   SECTION. 
Anthopyllite. 

An  orthorhombic  amphibole,  corresponding  to  the  orthorhombic 
pryoxene  group,  enstatite  —  bronzite — hy persthene.  An  iron-mag- 
nesium metasilicate,  (Mg,Fe)SiO3.  Rarely  in  distinct  crystals. 
Commonly  lamellar  or  fibrous.  Perfect  prismatic  cleavage.  Color 
gray  to  various  shades  of  green  and  brown.  A  comparatively  rare 
mineral,  occurring  in  mica-schist,  etc. 

Amphibole. 

Composition.  The  amphiboles  consist  of  a  series  of  minerals 
analogous  in  many  ways  to  the  pyroxenes.  They  are  chiefly 
metasilicates  of  calcium  and  magnesium  with  ferrous  iron  re- 
placing the  magnesium.  Other  molecules  are  at  times  intro- 
duced, in  which  are  the  alkalies,  aluminium  and  ferric  iron. 
The  more  important  varieties  of  amphibole  with  the  formulas 
assigned  to  them  follow. 

Tremolite,  CaMg3(Si03)4. 

Actinolite,  Ca(Mg,Fe)3(Si08)4. 

Hornblende,  CaMg3(SiO,)4  with  NasAl,(SiOOi  and  Mg2Al4- 
(Si06)2.  Ferrous  iron  is  isomorphous  with  the  magnesium  and 
ferric  iron  with  the  aluminium. 


238 


MANUAL  OF  MINERALOGY 


These  varieties  form  an  isomorphous  series  and  all  gradations 
between  them  occur. 

Crystallization.  Monoclinic.  Crystals  prismatic  in  habit; 
the  prism  faces  make  angles  of  55°  and  125°  with  each  other 
(compare  the  87°  and  93°  angles  of  pyroxene).  The  prism  zone 
shows,  in  addition  to  the  prism  faces,  usually  those  of  the 
clinopinacoid  and  sometimes  also  those  of  the  orthopinacoid. 


Fig.  304. 


Fig.  305. 


Prism  zone  frequently  vertically  striated  and  imperfectly  de- 
veloped. When  the  prism  faces  are  distinct,  the  cross  section 
of  the  crystal,  when  viewed  in  a  direction  parallel  to  the  vertical 
axis,  does  not  have  the  rectangular  shape  .shown  by  the  crystals 
of  pyroxene.  The  termination  of  the  crystals  is  almost  always 
formed  by  the  two  faces  of  a  low  clinodome  (Figs.  304  and  305). 

Structure.  In  crystals.  Often  bladed  and  frequently  in  radi- 
ating columnar  aggregates.  Sometimes  in  silky  fibers.  Coarse 
to  fine  granular.  Compact. 

Physical  Properties.  Perfect  prismatic  cleavage  at  angle  of 
125°,  often  yielding  a  splintery  surface.  H.  =  5-6.  G.  =  3-3.3. 
Vitreous  luster.  Often  with  silky  sheen  in  the  prism  zone.  Color 
varying  from  white  and  light  green  in  tremolite,  to  green  in 
actinolite,  through  dark  green  to  black  in  hornblende.  Color 
deepens  with  increase  in  the  amount  of  iron  present.  Trans- 
parent to  opaque. 

Tests.  Fusible  3-4.  Chemical  tests  same  as  for  pyroxene, 
which  see.  Told  from  pyroxene  by  its  better  prismatic  cleavage, 


AMPHIBOLE  239 

by  the  difference  in  the  prismatic  angle  and  by  the  characteristic 
presence  on  the  crystals  of  the  low  clinodome. 

Occurrence.  Amphibole  is  an  important  and  widely  distributed 
rock-making  mineral,  occurring  both  in  igneous  and  mctamorphic 
rocks,  being  particularly  characteristic,  however,  of  the  latter.  The 
fact  that  amphibole  frequently  contains  hydroxyl  and  fluorine  in- 
dicates that,  in  some  degree,  it  is  often  of  pneumatolytic  origin. 
Tremolite  is  most  frequently  found  in  impure,  crystalline,  dolomitic 
limestones,  where  it  has  been  formed  during  the  crystallization  of 
the  rock,  while  undergoing  metamorphism.  Actinolite  commonly 
occurs  in  the  crystalline  schists,  being  often  the  chief  constituent  of 
green-colored  hornblende-schists  and  greenstones.  Frequently  the 
amphibole  of  such  rocks  has  had  its  origin  in  the  pyroxene  contained 
in  the  igneous  rock  from  which  the  metamorphic  type  has  been 
derived.  Common  hornblende  is  found  in  igneous  rocks,  such  as 
granites,  syenites,  diorites,  gabbros,  and  in  some  peridotites;  it 
rarely  occurs  in  the  dark  traps  and  basalts.  It  also  occurs  in  the 
metamorphic  rocks,  such  as  gneisses  and  hornblende  schists. 

Notable  localities  for  the  occurrence  of  crystals  are:  tremolite 
from  Campolongo,  Tessin;  from  Russell,  Gouverneur,  Amity,  Pierre- 
pont,  De  Kalb,  etc.,  New  York;  actinolite  from  Greiner,  Zillerthal, 
Tyrol;  hornblende  from  Bilin,  Bohemia;  Monte  Somma,  Italy. 
Actinolite  frequently  comes  fibrous,  and  is  the  material  to  which 
the  name  asbestos  was  originally  given.  Has  been  found  in  the 
metamorphic  rocks  in  various  states  along  the  Appalachian  Moun- 
tains. Nephrite  is  a  tough,  compact  variety  of  actinolite  which 
supplies  much  of  the  material  known  as  jade  (see  also  under  jadeite). 
A  famous  locality  for  its  occurrence  is  in  the  Kuen  Lun  Mountains, 
on  the  southern  border  of  Turkestan. 

Names.  Tremolite  is  derived  from  the  Tremola  Valley  near 
St.  Gothard.  Actinolite  comes  from  two  Greek  words  meaning 
a  ray  and  stone,  in  allusion  to  its  frequently  somewhat  radiated 
structure. 

Uses.  The  fibrous  variety  is  used  to  some  extent  as  asbestos 
material.  The  fibrous  variety  of  serpentine  furnishes  more 
and  usually  a  better  grade  of  asbestos.  The  compact  variety, 
nephrite,  is  used  largely  for  ornamental  material  by  oriental 
peoples  and  is  called  jade. 

Among  the  other  rarer  monoclinic  members  of  the  Am- 
phibole Group  are  glaucophane,  NaAl(Si03)j.(Fe,Mg)SiOj; 


240 


MANUAL  OF  MINERALOGY 


riebeckite,  2NaFe(Si03)2.FeSi03;  crocidolite,  NaFe(Si03)2.FeSi03; 
arfvedsonite,  Na8(Ca,Mg)3(Fe,Mn)14(Al,Fe)2Si2i045. 

TRICLINIC   SECTION. 

The  only  member  of  the  Triclinic  Section  of  the  Amphibole 
Group  is  the  rare  mineral  cenigmatite,  Na4Fe9AlFe"/(Si,Ti)I2038. 


Beryl. 

Composition.  Be3Al2Si6Oi8.  Analyses  show  a  small  amount 
of  water.  Small  amounts  of  the  alkali  oxides,  often  in  part 
consisting  of  caesium  oxide,  frequently  replace  the  beryllium 
oxide. 

Crystallization.  Hexagonal.  Strong  prismatic  habit.  Fre- 
quently vertically  striated  and  grooved.  Forms  usually  present 


Fig.  306. 


Fig.  307. 


consist  only  of  prism  of  first  order  and  base  (Fig.  306).  Small 
pyramid  faces  of  both  the  first  and  second  orders  sometimes 
occur,  but  the  pyramid  faces  are  rarely  prominent  (Fig.  307). 
Dihexagonal  forms  quite  rare.  Crystals  frequently  of  consider- 
able size  with  rough  faces. 

Structure.  In  crystals.  Also  massive,  with  indistinct  colum- 
nar structure  or  granular. 

Physical  Properties.  H.  =  7.5-8.  G.  =  2.75-2.8.  Vitreous 
luster.  Color  commonly  bluish  green  or  light  yellow;  may 
be  deep  emerald-green,  golden  yellow,  pink,  white  or  colorless. 
Transparent  to  subtranslucent.  Frequently  the  larger,  coarser 


BERYL  241 

crystals  show  a  mottled  appearance  due  to  the  alternation  of 
clear  transparent  spots  with  cloudy,  almost  opaque  portions. 

Tests.  B.  B.  whitens  and  fuses  with  difficulty  at  5-5.5  to  an 
enamel.  Yields  a  little  water  on  intense  ignition.  Insoluble  in 
acids.  Recognized  usually  by  its  hexagonal  crystals,  its  hard- 
ness, color,  etc. 

Varieties.  Ordinary  Beryl.  In  coarse  translucent  to  opaque 
crystals  or  masses,  usually  of  a  pale  greenish  blue  or  yellow  color. 
Sometimes  in  very  large  crystals;  one  from  Graf  ton,  New  Hamp- 
shire, measured  over  4  feet  in  length  with  a  diameter  between 
20  and  30  inches,  weight  2900  pounds. 

Aquamarine.  Name  given  to  the  pale  greenish  blue  trans- 
parent stone.  Used  as  a  gem. 

Golden  Beryl.  A  deep  golden  yellow  variety,  which,  when 
clear,  is  used  as  a  gem. 

Rose  Beryl.  A  variety  varying  in  color  from  pale  pink  to 
deep  rose.  Beautiful  gem  material  from  Madagascar  has  been 
named  morganite. 

Emerald.  The  true  emerald  is  the  deep  green  transparent 
beryl  and  is  among  the  most  highly  prized  of  gems.  The  color 
is  due  to  small  amounts  .of  chromium. 

Occurrence.  Beryl,  although  containing  the  rare  element  beryl- 
lium, is  a  rather  common  and  widely  distributed  mineral.  It  occurs 
usually  as  an  accessory  mineral  in  pegmatite  veins.  It  is  also  found 
in  clay-slate  and  mica-schist.  Emeralds  of  gem  quality  occur  in  a 
dark  bituminous  limestone  at  Musa,  75  miles  northwest  of  Bogota, 
United  States  of  Colombia.  This  locality  has  been  worked  almost 
continually  since  the  middle  of  the  sixteenth  century,  and  has  fur- 
nished the  greater  part  of  the  emeralds  of  the  world.  Another 
famous  locality  for  emeralds  is  in  Siberia  on  the  river  Takovaya, 
45  miles  east  of  Ekaterinburg.  They  occur  in  a  mica-schist  asso- 
ciated with  phenacite,  chrysoberyl,  rutile,  etc.  Rather  pale  emeralds 
have  been  found  in  small  amount  from  Alexander  County,  North 
Carolina,  associated  with  the  green  variety  of  spodumene,  hiddenite. 
Beryl  of  the  lighter  aquamarine  color  is  much  more  common,  and 
is  found  in  gem  quality  in  Brazil,  Siberia,  and  many  other  localities. 
In  the  United  States  they  have  been  found  in  various  places  in  Maine, 
New  Hampshire,  Massachusetts,  Connecticut,  North  Carolina,  Colo- 
rado, etc.  The  golden  beryl  has  been  found  in  Maine,  Connecti- 
cut, North  Carolina  and  Pennsylvania;  also  in  Siberia  and  Ceylon. 


242  MANUAL  OF  MINERALOGY 

The  rose-colored  beryl  has  been  found  in  San  Diego  County,  Cali- 
fornia, associated  with  pink  tourmaline  and  the  pink  spodurnene, 
kunzite.  A  similar  occurrence  in  Madagascar  has  furnished  mag- 
nificent rose-colored  stones  (morganite). 

Use.  Used  as  a  gem  stone  of  various  colors.  The  emerald 
ranks  as  one  of  the  most  valuable  of  stones,  at  times  being  of 
much  greater  value  than  the  diamond.  Perfect  and  deeply 
colored  stones  have  been  sold  as  high  as  $1000  per  carat. 
Aquamarines  range  in  value  from  $1  to  $15  a  carat.  Golden 
beryls  bring  from  $1  to  $10  a  carat.  The  rose  beryl  is  valued 
from  $5  to  $20  a  carat. 

lolite.     Cordierite. 

A  complex  silicate  of  magnesium,  ferrous  iron  and  aluminium. 
Orthorhombic.  Usually  in  short  pseudohexagonal  twinned  crys- 
tals; as  embedded  grains;  massive.  Vitreous  luster.  Color  differ- 
ent shades  of  blue.  Most  commonly  altered  into  some  form  of 
mica,  becoming  opaque  and  of  various  shades  of  grayish  green. 
Found  as  an  accessory  mineral  in  granite,  gneiss  (cordierite  gneiss), 
schists,  etc. 

3.    ORTHOSILICATES. 

Nephelite. 

Composition.  Sodium-aluminium  silicate,  approximately 
NaAlSi04.  There  is  always  a  few  per  cent  of  potash  present, 
sometimes  also  lime,  replacing  the  soda. 

Crystallization.  Hexagonal.  Rarely  in  small  prismatic  crys- 
tals with  basal  plane;  sometimes  shows  pyramidal  planes. 

Structure.  Almost  invariably  massive,  compact,  and  in  em- 
bedded grains.  Massive  variety  often  called  elceolite. 

Physical  Properties.  Distinct  cleavage  parallel  to  prism. 
H.  =  5.5-6.  G.  =  2.55-2.65.  Vitreous  luster  in  the  clear  crys- 
tals to  greasy  luster  in  the  massive  variety.  Colorless,  white 
or  yellowish.  In  the  massive  variety  gray,  greenish  and  reddish. 
Transparent  to  opaque. 

Tests.  Fusible  at  4  to  a  colorless  glass.  B.  B.  gives  strong 
yellow  flame  of  sodium.  Readily  soluble  in  hydrochloric  acid 
and  on  evaporation  yields  a  silica  jelly. 


LAZURITE  243 

Alteration.  Easily  alters  into  various  other  minerals,  such  as 
the  zeolites,  natrolite,  analcite,  hydronephelite,  thomsonite;  also 
sodalite,  muscovite,  kaolin,  etcv 

Occurrence.  Nephelite  is  rarely  found  except  in  igneous  rocks. 
It  occurs  in  some  recent  lavas  as  glassy  crystals,  such  as  are  found 
in  the  lavas  of  Vesuvius.  The  opaque,  massive  or  coarsely  crystal- 
line variety  is  found  in  the  older  rocks  and  is  called  elaeolite.  Phono- 
lite,  elseolite-syenite  and  nephelite-basalt  are  important  rocks  in 
which  nephelite  is  an  essential  constituent.  It  is  only  to  be  found 
in  rocks  whose  magmas  contained  an  excess  of  soda  over  the  amount 
required  to  form  feldspar.  It  is  therefore  seldom  found  in  rocks 
that  contain  free  quartz.  Extensive  masses  of  nephelite  rocks, 
elaeolite-syenites,  are  found  in  Norway.  Massive  and  crystallized 
nephelite  is  found  at  Litchfield,  Maine,  associated  with  cancrinite. 
Found  at  Magnet  Cove,  Arkansas. 

Name.  Nephelite  is  derived  from  a  Greek  work  meaning  a 
cloud,  because  when  immersed  in  acid  the  mineral  becomes 
cloudy.  Elceolite  is  derived  from  the  Greek  word  for  oil,  in 
allusion  to  its  greasy  luster. 

Cancrinite,  H6Na6Ca(NaCOs)2Al8(Si04)9,  is  a  rare  mineral 
similar  to  nephelite  in  occurrence  and  associations. 

SODALITE    GROUP. 
Sodalite. 

Composition,  Na4(AlCl)Al2(SiO4)3.  Isometric.  Crystals  rare, 
usually  dodecahedrons.  Commonly  massive,  in  embedded  grains. 
Dodecahedral  cleavage.  H.=  5.5-6.  G.=  2.15-2.3.  Vitreous  lus- 
ter. Color  usually  blue,  also  white,  gray,  green.  Transparent  to 
opaque.  Fusible  at  3.5-4,  to  a  colorless  glass,  giving  a  strong 
yellow  flame  (sodium).  Soluble  in  hydrochloric  acid  and  gives 
gelatinous  silica  upon  evaporation.  Nitric  acid  solution  with  silver 
nitrate  gives  white  precipitate  of  silver  chloride.  A  comparatively 
rare  rock-making  mineral  associated  with  nephelite,  cancrinite,  etc., 
in  nephelite-syenites,  trachytes,  phonolites,  etc.  Found  in  transpar- 
ent crystals  in  the  lavas  of  Vesuvius.  Similar  minerals,  but  rarer  in 
their  occurrence,  are  hauynite,  (Na2.Ca)ji(Al.NaSO4)Al2(SiO4)3,  and 
noselite,  Na4(NaSO4 .  Al)Al2(SiO4)3. 

Lazurite.     Lapis-lazuli. 

Composition,  Na4(Al.NaSs)Al2(SiO4)3,  with  small  amounts  of  the 
Bodalite  and  haiiynite  molecules  in  isomorphous  replacement.  Iso- 


244  MANUAL  OF  MINERALOGY 

metric.  Crystals  rare,  usually  dodecahedral.  Commonly  massive, 
compact.  H.  =  5-5.5.  G.  =  2.4-2.45.  Vitreous  luster.  Color 
deep  azure-blue,  greenish  blue.  Translucent.  Fusible  at  3.5,  giv- 
ing strong  yellow  flame  (sodium).  Soluble  in  hydrochloric  acid 
with  slight  evolution  of  hydrogen  sulphide  gas,  and  gives  gelatinous 
silica  upon  evaporation.  A  rare  mineral,  occurring  usually  in  crys- 
talline limestones  as  a  product  of  contact  metamorphism.  Lapis- 
lazuli  is  usually  a  mixture  of  lazurite  with  small  amounts  of  calcite, 
pyroxene,  etc.  It  commonly  contains  small  disseminate  particles 
of  pyrite.  It  is  used  as  an  ornamental  stone,  for  carvings,  etc.  The 
best  quality  of  lapis-lazuli  comes  from  northeastern  Afghanistan. 
Also  found  at  Lake  Baikal,  Siberia,  and  in  Chile. 

GARNET  GROUP. 

Composition.  The  garnets  are  orthosilicates  which  conform 
to  the  general  formula  R3//R2/// (8104)3.  R"  may  be  calcium, 
magnesium,  ferrous  iron  and  manganese;  R'"  may  be  aluminium, 
ferric  iron  and  chromium.  The  formulas  of  the  chief  varieties 
are  given  below;  many  of  them,  however,  grade  more  or  less  into 
each  other. 

Grossularite, 
Pyrope, 
Almandite, 
Spessartite, 
Andradite,       Ca3Fe2(Si04)3. 
Uvarovite,        Ca3(Cr,Al)2(Si04)3. 

Crystallization.  Isometric.  Common  forms  dodecahedron 
(Fig.  308)  and  trapezohedron  (Fig.  309),  often  in  combination 
(Figs.  310  and  311).  Hexoctahedron  observed  at  times  (Fig. 
312).  Other  forms  rare. 

Structure.  Usually  distinctly  crystallized;  also  in  rounded 
grains;  massive  granular,  coarse  or  fine. 

Physical  Properties.  H.=  6.5-7.5.  G.  =  3.15-4.3,  varying 
with  the  composition.  Luster  vitreous  to  resinous.  Color  vary- 
ing with  composition;  most  commonly  red,  also  brown,  yellow, 
white,  green,  black.  White  streak.  Transparent  to  almost 
opaque. 

Tests.  With  the  exception  of  uvarovite,  all  garnets  fuse  at  3 
to  3.5;  uvarovite  is  almost  infusible.  The  iron  garnets,  alman- 


GARNET  GROUP 


245 


Fig.  308. 


Fig.  309. 


Fig.  310. 


Fig.  311. 


Fig.  312. 


dite  and  andradite,  fuse  to  magnetic  globules.'  Spessartite  when 
fused  with  sodium  carbonate  gives  a  bluish  green  bead  (manga- 
nese). Uvarovite  gives  a  green  color  to  salt  of  phosphorus  bead 
(chromium) .  Andradite  is  somewhat  difficultly  soluble  in  hydro- 
chloric acid  and  gelatinizes  imperfectly  on  evaporation.  All  the 
other  garnets  are  practically  insoluble  in  acids.  All  of  them, 
with  the  exception  of  uvarovite,  may  be  dissolved  in  hydrochloric 
acid  after  simple  fusion  and  the  solutions  will  gelatinize  on  evapo- 
ration. Garnets  are  usually  recognized  by  their  characteristic 
isometric  crystals,  their  hardness,  color,  etc.  It  frequently  re- 
quires an  analysis  to  positively  distinguish  between  the  different 
members  of  the  group. 

Varieties.  Grossularite,  Essonite,  Cinnamon  Stone.  Calcium- 
aluminium  garnet.  Often  contains  ferrous  iron  replacing  cal- 
cium and  ferric  iron  replacing  aluminium.  Color  white,  green, 


246  MANUAL  OF  MINERALOGY 

yellow,  cinnamon-brown,  pale  red.  Name  derived  from  the 
botanical  name  for  gooseberry,  in  allusion  to  the  light  green  color 
of  the  original  grossularite. 

Pyrope.  Precious  garnet  in  part.  Magnesium-aluminium 
garnet.  Calcium  and  iron  also  present.  Color  deep  red  to 
nearly  black.  Often  transparent  and  then  used  as  a  gem. 
Name  derived  from  Greek,  meaning  firelike.  Rhodolite  is  name 
given  to  a  pale  rose-red  or  purple  garnet,  corresponding  in  com- 
position to  two  parts  of  pyrope  and  one  of  almandite. 

Almandite.  Precious  garnet  in  part.  Common  garnet  in 
part.  Iron-aluminium  garnet.  Ferric  iron  replaces  aluminium 
and  magnesium  replaces  ferrous  iron.  Color  fine  deep  red,  trans- 
parent in  precious  garnet;  brownish  red,  translucent  to  opaque 
in  common  garnet.  Name  derived  from  Alabanda,  where  in 
ancient  times  garnets  were  cut  and  polished. 

Spessartite.  Manganese-aluminium  garnet.  Ferrous  iron  re- 
places the  manganese  and  ferric  iron  the  aluminium.  Color 
brownish  to  garnet-red. 

Andradite.  Common  garnet  in  part.  Calcium-iron  garnet. 
Aluminium  replaces  the  ferric  iron;  ferrous  iron,  manganese  and 
sometimes  magnesium  replace  the  calcium.  Color  various 
shades  of  yellow,  green,  brown  to  black.  Named  after  the 
Portuguese  mineralogist,  d'Andrada. 

Uvarovite.  Calcium-chromium  garnet.  Color  emerald-green. 
Named  after  Count  Uvarov. 

Occurrence.  Garnet  is  a  common  and  widely  distributed  min- 
eral, occurring  as  an  accessory  constituent  of  metamorphic  and 
sometimes  of  igneous  rocks.  Its  most  characteristic  occurrence  is 
in  mica-schists  (see  Fig.  C,  pi.  X),  hornblende-schists  and  gneisses. 
Found  in  pegmatite  veins,  more  rarely  in  granite  rocks.  Grossu- 
larite is  found  chiefly  as  a  product  of  contact  or  regional  metamor- 
phism  in  crystalline  limestones.  Pyrope  is  often  found  in  peridotite 
rocks  and  the  serpentines  derived  from  them.  Spessartite  occurs 
in  the  igneous  rock,  rhyolite.  Melanite,  a  black  variety  of  andra- 
dite,  occurs  mostly  in  certain  eruptive  rocks.  Uvarovite  is  found 
in  serpentine  associated  with  chromite.  Garnet  frequently  occurs 
as  rounded  grains  in  stream-  and  sea-sands. 

Almandite,  of  gem  quality,  is  found  in  northern  India,  Brazil, 
Australia,  and  in  several  localities  in  the  Alps.  Fine  crystals,  al- 


CHRYSOLITE  247 

though  for  the  most  part  too  opaque  for  cutting,  are  found  in  a  mica- 
schist  on  the  Stickeen  River,  Alaska.  Pyrope  of  gem  quality  is 
found  associated  with  clear  grains  of  chrysolite  (peridot)  in  the 
surface  sands  near  Fort  Defiance,  close  to  the  Utah-Arizona  state 
line.  Famous  localities  for  pyrope  gems  are  near  Teplitz  and  Bilin, 
Bohemia.  Grossularite  is  only  a  little  used  in  jewelry,  but  essonite 
or  cinnamon  stones  of  good  size  and  color  are  found  in  Ceylon.  A 
green  andradite,  known  as  demantoid,  cornes  from  the  Urals  and 
yields  fine  gems  known  as  Uralian  emeralds. 

Alteration.  Garnet  often  alters  to  other  minerals,  particu- 
larly talc,  serpentine  and  chlorite. 

Name.  Garnet  is  derived  from  the  Latin  granatus,  meaning 
like  a  grain.  Carbuncle,  an  old  name  for  garnet  and  other  red 
stones,  was  derived  from  the  Latin  word  carbo,  coal,  and  is  used 
at  present  to  designate  garnets  cut  in  oval  form- 
Use.  Chiefly  as  a  rather  inexpensive  gem  stone.  Sometimes 
ground  and  used  on  account  of  its  hardness  for  abrading  pur- 
poses, as  sand  for  sawing  and  grinding  stone,  or  for  making  sand- 
paper. 

CHRYSOLITE   GROUP. 

Chrysolite  or  Olivine.     Peridot. 

Composition.  Orthosilicate  of  magnesium,  with  varying 
amounts  of  ferrous  iron,  (Mg,Fe)2Si04.  The  ratio  between  the 
magnesium  and  iron  varies  widely. 

Crystallization.  Orthorhombic.  Crystals  usually  a  combi- 
nation of  prism,  macro-  and  brachypinacoids  and  domes,  pyra- 
mid and  base.  Often  flattened  parallel  to  either  the  macro-  or 
brachypinacoid. 

Structure.    Usually  in  embedded  grains  or  in  granular  masses. 

Physical  Properties.  H.  =  6.5-7.  G.  =  3.27-3.37.  Vitre- 
ous luster.  Olive  to  grayish  green,  brown.  Transparent  to 
translucent. 

Tests.  Infusible.  Rather  slowly  soluble  in  hydrochloric  acid 
and  yields  gelatinous  silica  upon  evaporation.  After  evapora- 
tion to  dryness,  take  up  residue  in  water  with  nitric  acid,  filter 


248  MANUAL  OF  MINERALOGY 

off  silica,  add  ammonia  in  excess  to  precipitate  ferric  hydroxide, 
filter,  add  ammonium  oxalate  to  prove  absence  of  calcium,  add 
sodium  phosphate  and  obtain  precipitate  of  ammonium-mag- 
nesium phosphate  (test  for  magnesium).  Distinguished  usually 
by  its  glassy  luster,  green  color  and  granular  structure. 

Occurrence.  A  rather  common  rock-making  mineral,  varying 
from  an  accessory  character  to  that  of  a  main  constituent  of  the  rock. 
It  is  found  principally  in  the  dark  colored  ferro-magnesium  igneous 
rocks  such  as  gabbro,  peridotite  and  basalt.  A  rock,  known  as 
dunite,  is  made  up  almost  wholly  of  chrysolite.  Found  also  at  times 
as  glassy  grains  in  meteorites.  Occasionally  in  crystalline  dolomitic 
limestones.  Associated  often  with  pyroxene,  the  plagioclase  feld- 
spars, magnetite,  corundum,  chromite,  serpentine,  etc.  The  trans- 
parent green  variety,  known  as  peridot,  and  used  as  a  gem  material, 
was  found  in  ancient  times  in  the  East,  the  exact  locality  for  the 
stones  not  being  known.  At  present  peridot  is  found  in  Upper 
Egypt,  near  the  Red  Sea,  and  in  rounded  grains  associated  with 
pyrope  garnet  in  the  surface  gravels  of  Arizona  and  New  Mexico. 
Crystals  of  chrysolite  are  found  in  the  lavas  of  Vesuvius.  Larger 
crystals,  altered  to  serpentine,  come  from  Snarum,  Norway.  Chryso- 
lite occurs  in  granular  masses  in  the  volcanic  bombs  in  the  Eifel. 
Dunite  rocks  are  found  at  Dun  Mountain,  New  Zealand,  and  with 
the  corundum  deposits  of  North  Carolina. 

Alteration.  Very  readily  altered  to  serpentine;  magnesium 
carbonate,  iron  ore,  etc.,  may  form  at  the  same  time. 

Name.  Chrysolite  means  golden  stone.  Olivine  derives  its 
name  from  the  usual  olive-green  color  of  the  mineral,  and  is 
the  term  usually  given  to  the  species  when  speaking  of  it  as  a 
rock-making  mineral.  Peridot  is  an  old  name  for  the  species. 

Use.  As  the  clear  green  variety,  known  usually  as  peridot,  it 
has  some  use  as  a  gem.  A  one-carat  stone  may  be  valued  up 
to  $5. 

Other  members  of  the  Chrysolite  Group  which  are  rarer  in 
occurrence  are  Monticellite,  CaMgSi04;  fosterite,  Mg2Si04;  and 
fayalite,  Fe2Si04.  Ordinary  chrysolite  is  intermediate  in  com- 
position between  the  last  two.  Another  member  which  has  been 
found  in  the  zinc  deposits  at  Franklin  Furnace,  New  Jersey,  is 
tephroite,  Mn2Si04. 


PHENACITE  249 

PHENACITE   GROUP. 
Willemite. 

Composition.  Zinc  orthosilicate,  Zn2Si04  =  Silica  27,  zinc 
oxide  73,  zinc  58.6.  Manganese  often  replaces  a  considerable 
part  of  the  zinc  (manganiferous  variety  called  troostite),  iron 
also  present  at  times  in  small  amount. 

Crystallization.  Hexagonal-rhombohedral ;  tri-rhombohedral. 
In  hexagonal  prisms  with  rhombohedral  terminations.  Faces 
of  third-order  rhombohedrons  rare. 

Structure.  Usually  massive  to  granular.  Rarely  crystallized 
except  in  variety  troostite. 

Physical  Properties.  H.  =  5.5.  G.  =  3.89-4.18.  Vitreous 
to  resinous  luster.  Color  white,  yellow-green,  blue,  when  pure; 
with  increase  of  manganese  becomes  apple-green,  flesh-red  and 
brown.  Transparent  to  opaque. 

Tests.  Willemite  infusible,  troostite  difficultly  fusible  (4.5-5). 
Soluble  in  hydrochloric  acid  and  yields  gelatinous  silica  on  evapo- 
ration. Gives  a  coating  of  zinc  oxide  when  heated  with  sodium 
carbonate  on  charcoal;  coating  yellow  when  hot,  white  when 
cold;  if  coating  is  moistened  with  cobalt  nitrate  and  heated  again 
it  turns  green.  Troostite  will  give  reddish  violet  color  to  the 
borax  bead  in  0.  F.  (manganese). 

Varieties.     Ordinary.     White  or  light  colored. 

Troostite.  Apple-green,  flesh-red  or  gray  color.  Contains  a 
considerable  amount  of  manganese.  Found  at  Franklin  Fur- 
nace, New  Jersey,  in  quite  large  crystals. 

Occurrence.  Found  at  Altenberg,  near  Moresnet,  Belgium,  and 
at  Franklin  Furnace,  New  Jersey.  At  the  latter  locality  it  is  asso- 
ciated with  franklinite  and  zincite,  often  in  an  intimate  mixture; 
also  embedded  in  calcite.  Occurs  sparingly  at  Merritt  Mine,  New 
Mexico. 

Use.    A  valuable  zinc  ore. 

Phenacite. 

Beryllium  orthosilicate,  Be2SiO4.  Hexagonal-rhombohedral;  tri- 
rhombohedral.  Crystals  usually  rhombohedral  in  form,  sometimes 
with  short  prisms.  Often  with  complex  development  and  fre- 


250 


MANUAL  OF  MINERALOGY 


quently  showing  the  faces  of  the  third-order  rhombohedron.  Pris- 
matic cleavage.  H.  =  7.5-8.  G.  =  2.96.  Vitreous  luster.  Color- 
less, white.  Transparent  to  translucent.  Infusible  and  insoluble. 
A  rare  mineral,  found  associated  usually  with  topaz,  chrysoberyl, 
beryl,  apatite,  etc.  Fine  crystals  are  found  at  the  emerald  mines 
in  the  Urals,  at  Pike's  Peak  and  Mount  Antero,  Colorado,  and  in 
Minas  Geraes,  Brazil.  Occasionally  cut  as  a  gem  stone. 

Dioptase,  H2CuSi04,  is  a  rare  mineral  belonging  in  this  group. 

SCAPOLITE    GROUP. 

A  group  of  minerals  varying  in  composition  by  the  isomor- 
phous  mixture  in  different  amounts  of  the  two  molecules, 
Ca4Al6Si6025(Me)  and  Na4Al3Si9024Cl,(Ma).  When  the  first 
molecule  (Me)  alone  is  present,  the  subname  of  meionite  is  used; 
when  the  second  molecule  (Ma)  represents  the  composition,  the 
name  marialite  is  used.  Wernerite,  or  common  scapolite }  shows 
a  combination  of  the  two  molecules  according  to  the  ratios  of 
Me  :  Ma  as  3  :  1  to  1  :  2;  while  mizzonite  corresponds  to  the 
ratios  of  Me  :  Ma  as  1  :  2  to  1  :  3.  Mixtures  in  all  proportions 
may  exist. 

Wernerite.     Common  Scapolite. 
Composition.     See  above. 

Crystallization.  Tetragonal;  tripyramidal.  Crystals  usually 
prismatic.  Prominent  forms  are  prisms  of  the  first  and  second 


Fig.  313. 


Fig.  314. 


orders,  pyramid  of  first  (Fig.  313).     Rarely  shows  the  faces  of 
the  pyramid  of  the  third  order  (Fig.  314). 


VESUVIANITE  251 

Structure.  Crystals  are  usually  coarse,  with  rough  faces  and 
often  large.  Also  massive,  granular,  or  with  faint  fibrous  appear- 
ance. 

Physical  Properties.  Imperfect  prismatic  cleavage.  H.= 
5-6.  G.  =  2.68.  Vitreous  luster  when  fresh  and  unaltered. 
Color  white,  gray  or  pale  green.  Transparent  to  opaque. 

Tests.  Fusible.  Varieties  containing  sodium  give  yellow 
flame  on  ignition.  Imperfectly  decomposed  by  hydrochloric 
acid,  yielding  separated  silica  but  without  the  formation  of  a 
jelly. 

Alteration.  Easily  altered  into  various  other  minerals,  such 
as  mica,  epidote,  talc,  kaolin,  etc. 

Occurrence.  The  scapolites  occur  in  the  crystalline  schists, 
gneisses  and  amphibolites,  and  in  many  cases  have  probably  been 
derived  by  alteration  from  plagioclase  feldspars.  They  also  charac- 
teristically occur  in  crystalline  limestones  formed  through  the  con- 
tact metamorphic  action  of  an  intruded  igneous  rock.  Associated 
with  light  colored  pyroxene,  amphibole,  garnet,  apatite,  titanite, 
zircon,  etc.  Found  in  various  places  in  Massachusetts;  Orange, 
Essex,  Lewis,  Jefferson  and  St.  Lawrence  counties,  New  York;  at 
Grenville,  Templeton,  Algona,  etc.,  Canada. 

The  other  members  of  the  group,  meionite,  mizzonite  and 
marialite,  are  much  rarer  in  occurrence.  Their  crystals  are 
usually  smaller  and  of  better  quality  than  those  of  wernerite. 
Meionite  and  missonite  are  found  in  limestone  blocks  on  Monte 
Somma. 


Vesuvianite. 

Composition.  A  basic  silicate  of  calcium  and  aluminium. 
Contains  usually  also  iron  oxides,  magnesia  and  fluorine.  For- 
mula uncertain. 

Crystallization.  Tetragonal.  Prismatic  in  habit.  Often  ver- 
tically striated.  Common  forms  are  prisms  of  first  and  second 
orders,  pyramid  of  first  order  and  base  (Figs.  315  and  316). 
Some  crystals  show  a  more  complex  development  with  other 
prisms,  pyramids,  ditetragonal  forms,  etc. 


252 


MANUAL  OF  MINERALOGY 


Structure.     In  crystals,  also  massive,  columnar,  granular. 

Physical  Properties.  H.  =  6.5.  G.  =  3.35-4.45.  Vitreous  to 
resinous  luster.  Usually  green  or  brown  in  color;  also  yellow, 
blue,  red.  Commonly  subtransparent  to  translucent.  Streak 
white. 


771 


I1 


Fig.  315. 


Tests.  Fuses  with  intumescence  to  a  greenish  or  brownish 
glass.  Only  slightly  soluble  in  acids  but  gelatinizes  in  hydro- 
chloric acid  after  simple  fusion. 

Occurrence.  Usually  to  be  found  in  crystalline  limestones  where 
they  have  been  metamorphosed  by  the  contact  action  of  igneous 
rocks.  Formed  probably  by  the  action  upon  impure  limestone  of 
hot  vapors  containing  water  and  fluorine  given  off  by  the  igneous 
rock.  Associated  with  other  contact  minerals,  such  as  garnet, 
pyroxene,  tourmaline,  chondrodite,  etc.  Was  originally  discovered 
in  the  ancient  ejections  of  Vesuvius  and  in  the  dolomitic  blocks  of 
Monte  Somma.  Important  localities  are,  Ala,  Piedmont;  Mon- 
zoni,  Tyrol;  Vesuvius;  Christiansand,  Norway;  Achmatoosk, 
Urals;  River  Wilui,  Siberia;  in  the  United  States,  at  Phippsburg 
and  Rumford,  Maine;  near  Amity,  New  York;  Inyo  County,  Cali- 
fornia; in  Canada  at  Litchfield,  Pontiac  County;  at  Grenville, 
Ontario;  at  Temple  ton,  Quebec. 


ZIRCON   GROUP. 

Zircon. 

Composition.     ZrSi04  =  Silica  32.8,  zirconia  67.2. 
Crystallization.     Tetragonal.    Crystals  usually  show  a  simple 
combination  of  prism  and  pyramid  of  the  first  order  (Figs.  317 


ZIRCON 


253 


and  318).    The  prism  of  the  second  order  and  a  ditetragonal 
pyramid  also  at  times  observed  (Fig.  319).    Base  very  rare. 


m 


Fig.  317. 


Fig.  318. 


Fig.  319. 


Crystal  forms  and  axial  ratio  prove  a  close  relationship  between 
zircon  and  cassiterite  and  rutile. 

Structure.     Usually  crystallized;   also  in  irregular  grains. 

Physical  Properties.  H.  =  7.5.  G.  =  4.68.  Luster  adaman- 
tine. Usually  nearly  opaque,  sometimes  transparent.  Color 
commonly  some  shade  of  brown;  also  colorless,  gray,  green,  red. 
Streak  uncolored.  High  refractive  index. 

Tests.  Infusible.  A  small  fragment  when  intensely  ignited 
glows  and  gives  off  a  white  light.  When  fused  with  sodium  car- 
bonate and  fusion  then  dissolved  in  dilute  hydrochloric  acid,  the 
solution  will  turn  a  piece  of  turmeric  paper  to  an  orange  color 
(zirconium).  Recognized  usually  by  its  characteristic  crystals, 
color,  luster,  hardness  and  high  specific  gravity. 

Occurrence.  Zircon  is  a  common  and  widely  distributed  acces- 
sory mineral  in  all  classes  of  igneous  rocks.  It  is  especially  frequent 
in  the  more  acid  types  such  as  granite,  syenite,  diorite,  etc.  Very 
common  in  nephelite-syenite.  It  is  the  first  one  among  the  silicates 
to  crystallize  out  from  a  cooling  magma.  Found  also  commonly  in 
crystalline  limestone,  in  gneiss,  schist,  etc.  Found  frequently  as 
rounded  pebbles  in  stream  sands;  often  with  gold.  Gem  zircons 
are  found  in  the  stream  sands  at  Matura,  Ceylon.  Occurs  in  the 
gold  gravels  in  the  Urals,  Australia,  etc.  Found  in  the  nephelite- 
syenites  of  Norway  and  of  Litchfield,  Maine.  In  considerable 
quantity  in  the  sands  of  Henderson  and  Buncombe  counties,  North 
Carolina. . 


254  MANUAL  OF  MINERALOGY 

Use.  When  transparent  serves  as  a  gem  stone,  valued  usu- 
ally at  $10  or  less  per  carat.  It  is  sometimes  colorless,  but  more 
often  of  a  brownish  and  red-orange  color,  called  hyacinth  or  ja- 
cinth. The  colorless,  yellowish  or  smoky  stones  are  called  jar- 
gon, because  while  resembling  the  diamond  they  have  little  value; 
and  thence  the  name  zircon.  Serves  as  the  source  of  zirconium 
oxide,  which  with  other  rare  oxides  is  used  in  the  manufacture 
of  the  Welsbach  incandescent  mantle. 

Thorite. 

Thorium  silicate,  ThSiO4,  always  with  some  water,  probably  from 
alteration,  and  sometimes  uranium.  Tetragonal.  Crystal  forms 
resemble  those  of  zircon.  Also  massive.  Resinous  to  greasy  luster. 
H.  =  4.5-5.  G.  =  4.8-5.2.  Color  orange-yellow,  brown,  black. 
Transparent  to  opaque.  Infusible.  Soluble  in  hydrochloric  acid 
and  gives  gelatinous  silica  upon  evaporation.  A  rare  mineral,  found 
chiefly  in  Norway,  commonly  altered.  For  uses  of  thorium  see 
under  monazite. 

DANBURITE-TOPAZ   GROUP. 
Danburite. 

Composition.     Calcium-boron  silicate,  CaB2(Si04)2. 

Crystallization.  Orthorhombic.  Prismatic  crystals,  closely 
related  to  those  of  topaz  in  habit. 

Structure.     Commonly  in  crystals. 

Physical  Properties.  H.=  7-7.25.  G.=  2.97-3.02.  Vitre- 
ous luster.  Colorless  or  pale  yellow.  Transparent  to  translu- 
cent. 

Tests.  Fusible  (3.5-4),  giving  a  green  flame.  Insoluble  in 
acids. 

Occurrence.  Found  in  crystals  at  Danbury,  Conn.;  Russell, 
New  York;  eastern  Switzerland;  Japan. 

Topaz. 

Composition.     (Al.F)2Si04  with  isomorphous(A1.0H)2Si04. 
Crystallization.    Orthorhombic.    In  prismatic  crystals  termi- 
nated by  pyramids,  domes  and  basal  plane  (Figs.  320,  321  and 


TOPAZ 


255 


322).     Often  highly  modified  (Fig.  323). 
tically  striated. 


Prism  faces  often  ver- 


Fig.  320. 


Fig.  321. 


Fig.  322. 


Fig.  323. 


Structure.  In  crystalline  masses;  also  granular,  coarse  or 
fine. 

Physical  Properties.  Perfect  basal  cleavage.  H.  =  8  (unusu- 
ally high) .  G .  =  3 . 52-3 . 57 .  Vitreous  luster.  Colorless,  yellow, 
yellow-brown,  pink,  bluish,  greenish.  Transparent  to  trans- 
lucent. 

Tests.  Infusible.  Insoluble.  Recognized  chiefly  by  its  crys- 
tals, its  basal  cleavage,  its  hardness  (8)  and  high  specific  gravity. 

Occurrence.  A  mineral  formed  through  the  agency  of  fluorine- 
bearing  vapors  given  off  during  the  last  stages  of  the  solidification 
of  igneous  rocks.  Found  in  cavities  in  rhyolite  lavas  and  granite; 
a  characteristic  mineral  in  pegmatite  veins.  Associated  with  otHer 
pneumatolytic  minerals,  as  tourmaline,  cassiterite,  apatite,  fluorite, 
etc.;  also  with  quartz,  mica,  feldspar.  Found  at  times  as  rolled 
pebbles  in  stream  sands.  Notable  localities  for  its  occurrence  are 
the  Nerchinsk  district  in  Siberia  in  large  wine-yellow  crystals;  from 
Adunchilon  and  Mursinka,  Siberia,  in  pale  blue  crystals;  from 
various  tin  localities  in  Saxony:  from  Minas  Geraes,  Brazil;  Mino 
Province,  Japan;  San  Luis  Potosi,  Mexico;  Pike's  Peak  and  Nath- 
rop,  Colorado;  Thomas  Range,  Utah;  Stoneham,  Maine. 

Name.  Derived  from  the  name  of  an  island  in  the  Red  Sea 
but  originally  probably  applied  to  some  other  species. 

Use.  As  a  gem  stone.  A  number  of  other  inferior  stones  are 
also  frequently  called  topaz.  The  color  of  the  stones  varies, 
being  colorless,  wine-yellow,  golden  brown,  pale  blue  and  pink. 
The  pink  color  is  usually  artificial,  being  produced  by  gently 


256  MANUAL  OF  MINERALOGY 

heating  the  dark  yellow  stones ;  it  is  permanent,  however.     The 
value  of  topaz  ranges  up  to  $10  for  a  one-carat  stone. 

Andalusite.     Chiastolite. 

Composition.  Aluminium  silicate,  Al2Si06=  Silica  36.8,  alu- 
mina 63.2. 

Crystallization.     Orthorhombic.    Usually  in   coarse,  nearly 
square  prisms.     Closely  related  crystallographically  to  topaz. 
Structure.     In  crystals;  massive. 

Physical  Properties.     H.=  7.5.    G.  =  3.16-3.20.     Vitreous 
luster.     Flesh-red,  reddish  brown,  olive-green.     Often  with  dark 
colored  carbonaceous   inclusions  forming  a 
cruciform  design,  lying  parallel  to  the  axial 
directions  (variety  chiastolite  or  made)   (see 
Fig.  324).     Transparent  to  opaque.     At  times 
strongly  dichroic,  appearing,  in  transmitted 
light,  green  in  one  direction  and  red  in  another. 
Tests.     Infusible.     Insoluble.     When  fine 
Fig.  324.  powder  is  made    into  a  paste  with  cobalt 

Cross  Section  of  Chi-  nitrate  and  intensely  ignited  it  turns  blue 

astohte  Crystal,  .    .  J 

(aluminium). 

Occurrence.  Found  in  schists.  Often  impure  and  commonly, 
at -least  partly  altered.  Notable  localities  are  in  Andalusia,  Spain; 
the  Tyrol;  in  water-worn  pebbles  from  Minas  Geraes,  Brazil.  In 
the  United  States  at  Standish,  Maine;  Westford,  Lancaster  and 
Sterling,  Massachusetts;  Litchfield  and  Washington,  Connecticut; 
Delaware  County,  Pennsylvania.  Chiastolite  is  found  in  Morihan, 
Brittany;  Bimbowrie,  South  Australia;  and  Massachusetts. 

Use.     When  clear  and  transparent  may  serve  as  a  gem  stone. 

Sillimanite.     Fibrolite. 

An  aluminium  silicate  like  andalusite,  Al2SiO5.  An  orthorhombic 
mineral,  occurring  in  long  slender  crystals  without  distinct  termina- 
tions; often  in  parallel  groups;  frequently  fibrous.  Perfect  pina- 
coidal  cleavage.  H.  =  6-7.  G.  =3.23.  Color  hair-brown  to  pale 
green.  Transparent  to  translucent.  Infusible.  Insoluble.  A 
comparatively  rare  mineral,  found  as  an  accessory  constituent  of 
metamorphic  rocks;  gneiss,  mica-schist,  etc. 


DATOLITE 


257 


Cyanite. 

Composition.  Aluminium  silicate,  like  andalusite  and  silli- 
manite,  Al2Si05. 

Crystallization.  Triclinic.  Usually  in  long  tabular  crystals; 
terminations  rare. 

Structure.     In  bladed  forms. 

Physical  Properties.  Perfect  pinacoidal  cleavage.  H.  =  5 
parallel  to  length  of  crystals,  7  at  right  angles  to  this  direction. 
G.  =  3.56-3.66.  Vitreous  to  pearly  luster.  Color  usually  blue, 
often  of  darker  shade  toward  the  center  of  the  crystal.  Also  at 
times  white,  gray  or  green. 

Tests.  Infusible.  Insoluble.  A  fragment  moistened  with 
cobalt  nitrate  and  ignited  assumes  a  blue  color  (aluminium). 
Characterized  by  its  bladed  crystals,  good  cleavage,  blue  color 
and  the  fact  that  it  is  softer  than  a  knife  in  the  direction  parallel 
to  the  length  of  the  crystals  but  harder  than  a  knife  in  the 
direction  at  right  angles  to  this. 

Occurrence.  An  accessory  mineral  in  gneiss  and  mica-schist, 
often  associated  with  garnet,  staurolite,  corundum,  etc.  Notable 
localities  for  its  occurrence  are  St.  Gothard,  Switzerland;  in  the 
Tyrol;  Litchfield,  Connecticut;  Chester  and  Delaware  counties, 
Pennsylvania;  Gaston,  Rutherford  and  Yancey  counties,  North 
Carolina. 

Name.     Derived  from  a  Greek  word  meaning  blue. 


Datolite. 


Composition.  A  basic  ortho- 
silicate  of  calcium  and  boron, 
Ca(B.OH)Si04  =  Silica  37.6,  bo- 
ron trioxide  21.8,  lime  35,  water 
5.6. 

Crystallization.  Monoclinic. 
Habit  varied.  Crystals  usually 
nearly  equidimensional  in  the 
three  axial  directions  and  often 
complex  in  development  (Fig. 
325). 


258  MANUAL  OF  MINERALOGY 

Structure.  In  crystals.  Coarse  to  fine  granular.  Sometimes 
compact. 

Physical  Properties.  H.  =  5-5.5.  G.  =  2.8-3.  Vitreous  lus- 
ter. Colorless,  white,  yellow.  Often  with  faint  greenish  tinge. 
Transparent  to  translucent,  rarely  opaque. 

Tests.  Fuses  at  2-2.5  to  a  clear  glass  and  colors  the  flame 
green  (boron).  Soluble  in  hydrochloric  acid  and  yields  gelati- 
nous silica  on  evaporation.  Gives  a  little  water  in  C.  T.  Char- 
acterized by  its  glassy  luster,  pale  green  color,  and  its  crystals 
with  many  and  usually  irregularly  developed  faces. 

Occurrence.  A  mineral  of  secondary  origin,  found  usually  in 
cavities  in  basalt  lavas  and  similar  rocks.  Associated  with  various 
zeolites,  with  calcite,  prehnite,  etc.  Occurs  associated  with  the 
trap  rocks  of  Massachusetts,  Connecticut  and  New  Jersey,  particu- 
larly at  Westfield,  Massachusetts,  and  Bergen  Hill,  New  Jersey. 
Found  associated  with  the  copper  deposits  of  Lake  Superior. 

Name.  Derived  from  a  Greek  work  meaning  to  divide,  allud- 
ing to  the  granular  structure  of  a  massive  variety. 

A  rare  mineral  belonging  to  the  Datolite  Group  is  gadolinite, 
Be3FeY2Si2010. 

EPIDOTE   GROUP. 

Zoisite. 

Composition.  HCa2Al3Si3Oi2  =  Silica  39.7,  alumina  33.7,  lime 
24.6,  water  2.0. 

Crystallization.  Orthorhombic.  Prismatic  crystals  usually 
without  distinct  terminations.  Vertically  striated. 

Structure.     In  crystals;  also  massive. 

Physical  Properties.  H.  =  6-6.5.  G.  =  3.25-3.37.  Vitre- 
ous luster.  Color  grayish  white,  green,  pink.  Transparent  to 
almost  opaque. 

Tests.  Fuses  at  3-4  with  intumescence  to  a  light  colored  slag. 
Yields  a  little  water  on  intense  ignition  in  C.  T. 

Occurrence.  Usually  in  crystalline  schists  with  one  of  the  am- 
phiboles.  Thulite  is  a  rose-pink  variety. 


ALLANITE  259 

Epidote. 

Composition.  Ca2(A1.0H)(Al,Fe)2(Si04)3.  Iron  occurs  in 
varying  amounts  isomorphous  with  both  the  aluminium  and  cal- 
cium. 

Crystallization.     Monoclinic.     Crystals  are  often  much  elon- 
gated parallel  to  the  ortho-axis  with  a  prominent  development 
of  the  faces  of  the  orthodome  zone, 
giving    them    a    prismatic    aspect.      </  c 

Striated  parallel  to  the  ortho-axis.      \ « 

Terminated  usually  only  at  one  end         \  r 

of    the    ortho-axis   and    most  com- 
monly by  the  two  faces  of  a  pyra-  Fig-  326- 
mid   (Fig.  326).     Twinning  shown  at  times. 

Structure.  Usually  coarse  to  fine  granular.  In  crystals.  At 
times  fibrous. 

Physical  Properties.  Perfect  basal  cleavage.  H.  =  6-7.  G.  = 
3.37-3.45.  Vitreous  luster.  Color  usually  pistachio-green  or 
yellowish  to  blackish  green,  sometimes  gray.  Transparent  to 
opaque.  Transparent  varieties  often  show  strong  dichroism, 
appearing  dark  green  in  one  direction,  and  brown  in  a  direction 
at  right  angles  to  the  first. 

Tests.  Fuses  at  3-4  with  intumescence  to  a  black  slag.  On 
intense  ignition  in  C.  T.  yields  a  little  water. 

Occurrence.  Epidote  occurs  commonly  in  the  crystalline  meta- 
morphic  rocks;  as  gneiss,  amphibolite  and  various  schists.  Is 
formed  frequently  also  during  the  metamorphism  of  an  impure 
limestone.  Is  the  product  of  alteration  of  such  minerals  as  feldspar, 
pyroxene,  amphibole,  biotite,  scapolite,  etc.  Often  associated  with 
chlorite.  Notable  localities  for  its  occurrence  in  fine  crystals  are 
Knappenwand,  Unterzulzbachthal,  Tyrol;  Bourg  d'Oisans,  Dau- 
phine,  the  Ala  Valley  and  Traversella,  Piedmont;  Prince  William 
Island,  Alaska;  Haddam,  Connecticut;  Riverside,  California. 

Allanite. 

A  mineral  similar  to  epidote  in  composition,  but  containing  con- 
siderable amounts  of  the  cerium  metals,  cerium,  lanthanum  and 
didymium,  and  sometimes  with  smaller  amounts  of  yttrium  and 
erbium.  Composition  complex  and  widely  varying.  Monoclinic, 


260  MANUAL  OF  MINERALOGY 

habit  of  crystals  often  similar  to  epidote.  Commonly  massive  and 
in  embedded  grains.  H.  =  5.5-6.  G.  =  3.5-4.2.  Submetallic  to 
pitchy  and  resinous  luster.  Brown  to  pitch-black  color.  Fuses  at 
2.5  with  intumescence.  Sometimes  magnetic  after  heating.  Gelati- 
nizes in  acids.  Occurs  as  a  minor  accessory  constituent  in  many 
igneous  rocks.  Frequently  associated  with  epidote. 


Axinite. 

Composition.     Ca7Al4B2(Si04)8;  with  varying  amounts  of  fer- 
rous iron,  manganese,  magnesium  and  hydrogen  isomorphous 
with  the  calcium,  and  ferric  iron  with  the 
aluminium. 

Crystallization.  Triclinic.  Crystals 
usually  thin  with  sharp  edges  but  varied 
in  habit  (Fig.  327). 

Structure.     In    crystals.     Massive,   la- 
mellar to  granular. 
Fig.  327.  Physical  Properties.     Pinacoidal  cleav- 

age.     H.=  6.5-7.      G.=  3.27-3.35.      Vitreous  luster.      Color 
clove-brown,  gray,  green,  yellow.     Transparent  to  opaque. 

Tests.  Fusible  at  2.5-3  with  intumescence.  When  mixed 
with  potassium  bisulphate  and  fluorite  and  the  mixture  heated 
on  platinum  wire  gives  a  green  flame  (boron). 

Occurrence.  Notable  localities  for  its  occurrence  are  Bourg 
d'Oisans  in  Dauphine;  St.  Just,  Cornwall;  Obira,  Japan;  Franklin 
Furnace,  New  Jersey,  etc. 

Name.  Derived  from  a  Greek  word  meaning  ax,  in  allusion 
to  the  wedgelike  shape  of  the  crystals. 

Prehnite. 

Composition.  H2Ca2Al2Si30i2  =  Silica  43.7,  alumina  24.8, 
lime  27.1,  water  4.4. 

Crystallization.     Orthorhombic.     Distinct  crystals  rare. 

Structure.  Reniform,  stalactitic.  In  rounded  groups  of  tab- 
ular crystals. 

Physical  Properties.  H.  =  6-6.5.  G.  =  2.8-2.95.  Vitreous 
luster.  Color  usually  light  green,  passing  into  white.  Trans- 
lucent. 


CALAMINE 


261 


Tests.  Fuses  at  2.5  with  intumescence  to  an  enamel.  Heated 
in  C.  T.  yields  water.  Slowly  acted  upon  by  hydrochloric  acid 
but  gelatinizes  after  simple  fusion. 

Occurrence.  As  a  mineral  of  secondary  origin  lining  amygdaloidal 
cavities  in  basalt,  etc.  Associated  with  zeolites,  datolite,  pectolite, 
calcite,  etc.  Occurs  in  the  United  States  at  Farmington,  Connecti- 
cut; Paterson  and  Bergen  Hill,  New  Jersey;  Somerville,  Massa- 
chusetts; Lake  Superior  copper  district.  Found  also  in  various 
European  localities. 

4.    SUBSILICATES. 
HUMITE    GROUP. 

The  three  minerals,  humite,  Mg3[Mg(F,OH)]2[Si04]2,  chondro- 
^e,-Mg6[Mg(F,OH)]2[Si04]3,  and  clinohumite,  Mg7[Mg(F.OH)]2- 
[Si04]4,  are  closely  related  chemically  and  crystallographically. 
They  are  characteristically  found  in  crystalline  limestones. 
Chondrodite  is  the  most  common  in  occurrence. 


Ilvaite,  or  lievrite,  HCaFe2/'Fe/"Si209,  is  a  rare  mineral  be- 
longing in  this  section. 

Calamine. 

Composition.     Silicate  of  zinc,  H2(Zn20)Si04  =  Silica  25,  zinc 
oxide  67.5,  water  7.5. 

Crystallization.  Orthorhombic ;  hemimorphic.  Crystals  usu- 
ally tabular  parallel  to  the  brachypinacoid.  They  show  prism 
faces  and  are  terminated  above  usually  by  a 
combination  of  macrodomes  and  brachy- 
domes  and  base,  and  below  by  a  pyramid 
(Fig.  328). 

Structure.  Usually  in  crystal  groups  with 
the  individuals  attached  at  their  lower  (pyra- 
midal) ends  and  lying  with  their  brachypinacoid 
faces  in  common.  Crystals  often  divergent, 
giving  rounded  groups  with  slight  reentrant 
notches  between  the  individual  crystals,  form- 
ing knuckle  or  coxcomb  masses.  Also  mammillary,  stalactitic, 
massive  and  granular. 


Fig.  328. 


262  MANUAL  OF  MINERALOGY 

Physical  Properties.  Prismatic  cleavage.  H.  =  4.5-5.  G.= 
3.4-3.5.  Vitreous  luster.  Color  white,  sometimes  with  faint 
bluish  or  greenish  shade;  also  yellow  to  brown.  Transparent 
to  translucent.  Strongly  pyroelectric. 

Tests.  Fusible  with  difficulty  at  5.  Soluble  in  hydrochloric 
acid  and  yields  gelatinous  silica  on  evaporation.  Fused  on 
charcoal  with  sodium  carbonate  gives  a  nonvolatile  coating  of 
zinc  oxide  (yellow  when  hot,  white  when  cold).  Gives  water  in 
C.  T.  Recognized  usually  by  the  characteristic  grouping  of  its 
crystals,  but  may  be  obscure  and  to  be  determined  only  by  above 
tests. 

Occurrence.  A  mineral  of  secondary  origin,  found  in  the  oxidized 
portion  of  zinc  deposits,  associated  with  smithsonite,  sphalerite, 
cerussite,  anglesite,  galena,  etc.  Usually  with  limestone  rocks. 
Occurs  at  Altenberg  and  Moresnet,  Belgium;  Aix-la-Chapelle,  Ger- 
many; in  Carinthia;  Hungary;  Cumberland,  England;  Sterling 
Hill,  near  Ogdensburg,  New  Jersey;  Friedensville,  Pennsylvania; 
Wythe  County,  Virginia;  with  the  zinc  deposits  of  southwestern 
Missouri. 

Name.  Supposed  to  be  derived  from  cadmia,  a  name  given 
by  the  ancients  to  the  silicate  and  carbonate  of  zinc.  The 
mineral  is  called  by  English  mineralogists  hemimorphite  or  elec- 
tric calamine. 

Use.     An  ore  of  zinc. 

Tourmaline. 

Composition.  A  complex  silicate  of  boron  and  aluminium,  con- 
taining varying  amounts  of  ferrous  iron,  magnesium,  magnanese, 
calcium,  sodium,  potassium,  lithium,  hydroxyl  and  fluorine. 

Crystallization.  Hexagonal-rhombohedral ;  hemimorphic. 
Crystals  usually  prismatic,  vertically  striated.  A  triangular 
prism,  with  three  faces,  prominent,  which  with  the  tendency  of 
the  prism  faces  to  be  vertically  striated  and  to  round  into  each 
other  gives  the  crystals  usually  a  cross  section  like  a  spherical 
triangle  (Fig.  329).  Crystals  are  commonly  terminated  by  base 
and  low  positive  and  negative  rhombohedrons ;  sometimes 
scalenohedrons  are  present.  When  the  crystals  are  doubly  ter- 


TOURMALINE 


263 


minated  they  usually  show  different  forms  at  the  opposite  ends 
of  the  vertical  axis  (hemimorphism)  (Figs.  330  and  331). 


Fig.  329. 


Fig.  330. 


Fig.  331. 


Structure.  Usually  in  crystals.  Sometimes  massive  com- 
pact; also  coarse  to  fine  columnar,  either  radiating  or  parallel. 

Physical  Properties.  Vitreous  to  resinous  luster.  Color 
varied,  depending  upon  the  composition.  Common  tourmaline 
with  much  iron  is  black,  sometimes  brown.  More  rarely  light 
colored  in  fine  shades  of  red,  pink,  green,  blue,  yellow,  etc. 
Rarely  white  or  colorless.  A  single  crystal  may  show  several 
different  colors  either  arranged  in  concentric  bands  about  the 
center  of  the  crystal  or  in  transverse  layers  along  its  length. 
Strongly  pyroelectric ;  i.e.,  when  cooling  from  being  heated  to 
about  100°  C.  it  develops  positive  electricity  at  one  end  of  the 
crystal  and  negative  at  the  other,  which  enables  the  crystal  to 
attract  and  hold  bits  of  paper,  etc.  Strongly  dichroic;  i.e.,  light 
traversing  the  crystal  in  one  direction  may  be  of  quite  a  different 
color  or  shade  of  color  from  that  traversing  the  crystal  in  a 
direction  at  right  angles  to  the  first.  H.  =  7-7.5;  G.  =  2.98-3.2. 

Tests.  To  be  recognized  usually  by  the  characteristic  rounded 
triangular  cross  section  of  the  crystals;  absence  of  prismatic 
cleavage,  coal-like  fracture  of  black  variety. 

Occurrence.  Tourmaline  is  one  of  the  most  common  and  charac- 
teristic minerals  formed  by  pneumatolytic  action.  That  is,  it  is  a 
mineral  that  has  been  formed  at  high  temperatures  and  pressures 
through  the  agency  of  vapors  carrying  boron,  fluorine,  etc.  It  is 
found,  therefore,  commonly  as  an  accessory  mineral  in  pegmatite 


264 


MANUAL  OF  MINERALOGY 


veins,  or  dikes,  occurring  with  granite  intrusions.  Associated  with 
the  ordinary  minerals  of  granite  pegmatite,  orthoclase,  albite,  quartz 
and  muscovite;  also  with  lepidolite,  beryl,  apatite,  fluorite,  etc. 
Found  also  as  an  accessory  mineral  in  metamorphic  rocks,  such  as 
gneisses,  schists  and  crystalline  limestones. 

The  black  tourmaline  is  of  widespread  occurrence  as  an  accessory 
mineral  in  metamorphic  rocks.  The  light  colored  gem  varieties 
are  found  in  the  pegmatite  dikes.  Famous  localities  for  the  occur- 
rence of  the  gem  tourmalines  are  the  island  of  Elba;  in  the  state  of 
Minas  Geraes,  Brazil;  Ural  Mountains  near  Ekaterinburg;  Mada- 
gascar; Paris  and  Auburn,  Maine;  Haddam  Neck,  Connecticut;  Mesa 
Grande,  Pala,  Rincon  and  Ramona  in  San  Diego  County,  California. 

Name.  The  name  tourmaline  comes  from  turamali,  a  name 
given  to  the  early  gems  from  Ceylon. 

Use.  Tourmaline  forms  one  of  the  most  beautiful  of  the  semi- 
precious gem  stones.  The  color  of  the  stones  varies,  the  princi- 
pal shades  being  olive-green,  pink  to  red  and  blue.  Sometimes 
a  stone  is  so  cut  as  to  show  different  colors  in  different  parts.  The 
green-colored  stones  are  usually  known  by  the  mineral  name, 
tourmaline,  or  as  Brazilian  emeralds.  The  red  or  pink  stones 
are  known  as  rubellite,  while  the  rarer  dark  blue  stones  are  called 
indicolite. 

Staurolite. 

Composition.  A  ferrous  iron-aluminium  silicate,  HAl6Fe- 
Si2013. 

Crystallization.  Orthorhombic.  Habit  prismatic,  showing 
usually  a  combination  of  prism  with  large  angle  (130°),  brachy- 


Fig.  332.  Fig.  333.  Fig.  334. 

pinacoid,  base  and  macrodome  (Fig.  332).      Cruciform  twins 
very  common;  of  two  types,  (1)  in  which  the  two  individuals 


APOPHYLLITE  265 

cross  at  nearly  90°  (Fig.  333),  (2)  in  which  they  cross  at  nearly 
60°  (Fig.  334).  Sometimes  both  types  are  combined  in  one 
crystal. 

Structure.     Usually  in  crystals. 

Physical  Properties.  H.  =  7-7.5.  G.  =  3.65-3.75.  Resin- 
ous to  vitreous  luster,  for  pure  and  fresh  material;  often  dull  to 
earthy  when  altered  or  impure.  Color  red-brown  to  brownish 
black.  Translucent  to  opaque. 

Tests.  Infusible.  Insoluble.  On  intense  ignition  in  C.  T. 
yields  a  little  water.  Often  very  impure.  Recognized  by  its 
characteristic  crystals  and  twins. 

Occurrence.  Staurolite  is  an  accessory  mineral  in  metamorphic 
rocks;  in  crystalline  schists,  slates,  and  sometimes  in  gneisses. 
Often  associated  with  garnet,  cyanite,  sillimanite,  tourmaline.  No- 
table localities  for  its  occurrence  are  Monte  Campini,  Switzerland; 
in  Brittany;  Minas  Geraes,  Brazil;  Windham,  Maine;  Francoriia 
and  Lisbon,  New  Hampshire;  Chesterfield,  Massachusetts;  Fannin 
County,  Georgia. 

Name.  Derived  from  a  Greek  word  meaning  cross,  in  allusion 
to  its  cruciform  twins. 

Use.  Occasionally  a  transparent  stone  from  Brazil  is  cut  as  a 
gem. 

HYDROUS  SILICATES. 

ZEOLITE   DIVISION. 
INTRODUCTORY   SUBDIVISION. 

Apophyllite. 

Composition.  HyKCa/SiOs^.^^O.  Usually  contains  a 
small  amount  of  fluorine. 

Crystallization.  Tetragonal.  Usually  shows  a  combination 
of  prism  of  second  order,  pyramid  of  first  and  basal  plane  (Figs. 
335  and  336).  Small  faces  of  a  ditetragonal  prism  sometimes 
observed  (Fig.  337).  Prism  faces  show  vertical  striations  and 
have  a  vitreous  luster,  while  base  shows  pearly  luster.  Crys- 
tals may  resemble  an  isometric  combination  of  cube  and  octa- 


266 


MANUAL  OF  MINERALOGY 


hedron,  but  are  shown  to  be  tetragonal  by  difference  in  luster 
between  faces  of  prism  and  base. 


Fig.  335. 


Fig.  336. 


Fig.  337. 


Structure.     In  crystals;   also  massive  and  lamellar. 

Physical  Properties.  Perfect  basal  cleavage.  H.  =  4.5-5. 
G.  =  2.3-3.4.  Luster  of  base  pearly,  other  faces  vitreous. 
Color  usually  colorless,  white  or  grayish;  may  show  pale  shades 
of  green,  yellow,  rose.  Usually  transparent,  rarely  nearly 
opaque. 

Tests.  Fuses  easily  with  swelling  to  a  white  vesicular  enamel. 
Colors  the  flame  pale  violet  (potassium).  Yields  16  per  cent 
of  water  in  C.  T.  Decomposed  by  hydrochloric  acid  with 
separation  of  silica  but  without  the  formation  of  a  jelly.  Solu- 
tion gives  little  or  no  precipitate  with  ammonia  but  gives  an 
abundant  white  precipitate  with  ammonium  carbonate  (calcium 
carbonate) .  Recognized  usually  by  its  crystals,  color,  luster  and 
basal  cleavage. 

Occurrence.  Occurs  commonly  as  a  secondary  mineral  lining 
cavities  in  basalt  and  related  rocks.  Associated  with  various  zeo- 
lites, with  calcite,  datolite,  pectolite,  etc.  Found  in  fine  crystals  at 
Bergen  Hill,  New  Jersey;  Cliff  Mine,  Lake  Superior  copper  district; 
Table  Mountain,  near  Golden,  Colorado;  mercury  mines,  New  Al- 
maden,  California;  Nova  Scotia;  Guanjuato,  Mexico;  near  Bombay, 
India;  Andreasberg,  Harz  Mountains;  Faroer  Islands;  Iceland; 
Greenland,  etc. 

Name.  Apophyllite,  named  from  two  Greek  words  meaning 
to  get  leaves,  because  of  its  tendency  to  exfoliate  when  ignited. 


HARMOTONE  267 

ZEOLITES. 

The  zeolites  form  a  large  family  of  hydrous  silicates  which 
show  close  similarities  in  composition  and  in  their  associations 
and  mode  of  occurrence.  They  are  silicates  of  aluminium  with 
sodium  and  calcium  as  the  important  bases.  They  average 
from  3.5  to  5.5  in  hardness  and  from  2  to  2.4  in  specific  gravity. 
Many  of  them  fuse  readily  with  marked  intumescence,  hence  the 
name  zeolite,  from  two  Greek  words  meaning  to  boil  and  stone. 
They  are  secondary  minerals  found  characteristically  in  cavities 
and  veins  in  basic  igneous  rocks. 

Heulandite. 

Composition,  H4CaAl2(SiO3)6.3H2O.  Monoclinic,  but  crystals 
often  simulate  orthorhombic  symmetry.  Clinopinacoid  prominent, 
having  often  a  diamond  shape.  Perfect  cleavage  parallel  to  clino- 
pinacoid.  H.  =  3.5-4.  G.  =  2.15-2.2.  Vitreous  luster,  except  on 
clinopinacoid,  which  is  pearly.  Color  white,  yellow,  red.  Trans- 
parent to  almost  opaque.  Fusible  (3)  with  intumescence.  Decom- 
posed by  hydrochloric  acid  with  separation  of  silica.  Water  in  C.  T. 
A  mineral  of  secondary  origin  found  in  cavities  of  basic  igneous 
rocks  associated  with  other  zeolites,  calcite,  etc.  Found  in  notable 
quality  in  Iceland;  the  Faroer  Islands;  British  India;  Nova  Scotia. 

Phillipsite. 

Composition,  (K2,Ca)Al2Si4Oi2.4£H2O.  Monoclinic.  Crystals 
are  uniformly  penetration  twins  but  often  appearing  to  be  tetragonal 
or  orthorhombic  in  form.  Cleavage  parallel  to  base  and  clinopina- 
coid. H.  =  4-4.5.  G.  =  2.2.  Vitreous  luster.  White  or  reddish 
in  color.  Translucent  to  opaque.  Fuses  at  3  to  a  white  enamel. 
Gelatinizes  with  hydrochloric  acid.  Water  in  C.  T.  A  secondary 
mineral  found  in  cavities  of  igneous  rocks  associated  with  other 
zeolites,  etc. 

Harmotone. 

A  barium  zeolite  having  the  composition  (K2,Ba)Al2Si4Oi2.3H2O. 
Monoclinic.  Crystals  are  uniformly  cruciform  penetration  twins. 
Perfect  cleavage  parallel  to  clinopinacoid.  H.  =  4.5.  G.  =  2.4- 
2.5.  Vitreous  luster.  Colorless  or  white.  Translucent.  Fuses  at 
3.  Decomposed  by  hydrochloric  acid  with  separation  of  silica. 
Addition  of  sulphuric  acid  to  hydrochloric  acid  solution  gives  a 


268  MANUAL  OF  MINERALOGY 

white  precipitate  of  barium  sulphate.  Water  in  C.  T.  A  mineral  of 
secondary  origin,  occurring  in  cavities  of  basic  igneous  rocks,  asso- 
ciated with  other  zeolites,  calcite,  etc. 

Stilbite.     Desmine. 

Composition.     (Na2,Ca)Al2Si6Oi6.6H20. 
Crystallization.    Monoclinic.    Uniformly  in  cruciform  twins. 
Commonly  tabular  parallel  to  clinopinacoid.     Crys- 
tals usually  in  sheaflike  aggregates  (Fig.  338). 

Structure.  In  crystal  groups,  divergent  or  radi- 
ated. 

Physical  Properties.  Perfect  cleavage  parallel 
to  clinopinacoid.  H.  =  3.5-4.  G.  =  2.1-2.2.  Vit- 
reous luster;  pearly  on  clinopinacoid.  Color  white, 
yellow,  brown,  red.  Translucent. 

Tests.     Fuses  with  intumescence  at  3.     Decom- 
posed by  hydrochloric  acid  with  separation  of  silica 
but  without  the  formation  of  a  jelly.    Water  in 
Fig.  338.       Q  ,p      Characterized  chiefly  by  its  cleavage,  pearly 
luster  on  the  cleavage  face  and  common  sheaflike  groups  of 
crystals. 

Occurrence.  A  mineral  of  secondary  origin  found  in  amygdaloidal 
cavities  in  basalts  and  related  rocks.  Found  associated  with  other 
zeolites,  calcite,  etc.  Notable  localities  for  its  occurrence  are  Poo- 
nah,  India;  IsleofSkye;  Faroer  Islands;  Kilpatrick,  Scotland;  Ice- 
land; Nova  Scotia. 

Name.     Derived  from  a  Greek  word  meaning  luster. 

Laumontite. 

A  zeolite  with  composition  H4CaAl2Si4Oi4.2H2O.  Monoclinic. 
In  prismatic  crystals  with  oblique  terminations;  columnar.  Cleav- 
age parallel  to  prism  and  clinopinacoid.  H.  =  3.5-4.  G.  =  2.25- 
2.35.  Vitreous  to  pearly  luster.  Color  white  or  gray.  Alters  on 
exposure,  becoming  opaque  and  pulverulent.  Fusible  (2.5).  Gelat- 
inizes in  acids.  Water  in  C.  T.  Found  as  a  mineral  of  secondary 
origin  in  cavities  of  basic  igneous  rocks,  associated  with  other  zeo- 
lites, etc. 


ANALCITE  269 

Chabazite. 

Composition.  Usually  corresponds  to  (Ca,Na2)Al2Si40i2.6H2O 
but  different  analyses  show  considerable  variation  from  this 
formula,  so  that  the  composition  is  still  uncertain. 

Crystallization.     Hexagonal-rhombohedral.     Common  form 
is  the  simple  rhombohedron  r,  having  nearly  cubic  angles.    May 
show  several  different  rhombo- 
hedrons   (Fig.  339).     Often   in 
penetration  twins. 

Structure.  Usually  in  crys- 
tals. 

Physical  Properties.  H.  = 
4-5.  G.=  2.05-2.15.  Vitreous 
luster.  Color  white,  yellow, 
flesh-red.  Transparent  to  trans- 
lucent. Fl«- 339- 

Tests.  Fuses  with  swelling  at  3.  Decomposed  by  hydro- 
chloric acid  with  the  separation  of  silica  but  without  the  for- 
mation of  a  jelly.  Solution  after  filtering  off  silica  gives  pre- 
cipitate of  aluminium  hydroxide  with  ammonia,  and  in  filtrate 
ammonium  carbonate  gives  white  precipitate  of  calcium  carbo- 
nate. Gives  much  water  in  C.  T.  Recognized  usually  by  its 
crystals. 

Occurrence.  A  mineral  of  secondary  origin  found  usually  with 
other  zeolites,  lining  amygdaloidal  cavities  in  basalt.  Notable 
localities  for  its  occurrence  are  the  Faroer  Islands;  Greenland  and 
Iceland;  the  Giant's  Causeway,  Ireland;  at  Aussig,  Bohemia;  in 
Nova  Scotia,  etc. 

Name.  Chabazite  is  derived  from  a  Greek  word  which  was 
an  ancient  name  for  a  stone. 

Gmelintie,  (Na2,Ca)Al2Si4Oi2.6H20,  is  closely  related  to  chaba- 
zite  but  rarer  in  occurrence. 

Analcite. 

Composition.  Hydrous  sodium-aluminium  metasilicate, 
NaAlSi206.H20  =  Silica  54.5,  alumina  23.2,  soda  14.1,  water 
8.2.  Note  similarity  in  composition  to  leucite,  KAlSi2Oe. 


270  MANUAL  OF  MINERALOGY 

Crystallization.  Isometric.  Usually  in  trapezohedrons  (Fig. 
340).  Cubes  with  trapezohedral  truncations  also  known  (Fig. 
341). 


Fig.  340.  Fig.  341. 

Structure.     Usually  in  crystals,  also  massive  granular. 

Physical  Properties.  H.  =  5-5.5.  G.  =  2.27.  Vitreous  lus- 
ter. Colorless  or  white.  Transparent  to  nearly  opaque. 

Tests.  Fusible  at  3.5,  becoming  first  opaque  and  then  a  clear 
glass.  Colors  the  flame  yellow  (sodium).  Decomposed  by  hy- 
drochloric acid  with  the  separation  of  silica  without  the  forma- 
tion of  a  jelly.  Gives  water  in  C.  T.  Usually  recognized  by  its 
crystals  and  its  vitreous  luster. 

Occurrence.  Commonly  a  secondary  mineral,  formed  by  the 
action  of  hot  circulating  waters,  and  is  to  be  found  deposited  in  the 
cavities  of  igneous  and  especially  volcanic  rocks.  Associated  with 
calcite,  and  various  zeolites  and  related  minerals.  Fine  crystals 
found  at  Bergen  Hill,  New  Jersey;  in  the  Lake  Superior  copper 
district;  at  Table  Mountain,  near  Golden,  Colorado;  at  Cape 
Blomidon,  Nova  Scotia;  in  the  Cyclopean  Islands  near  Sicily;  in 
the  Fassathal,  Tyrol;  on  the  Faroer  Islands;  in  Iceland. 

Name.  Derived  from  a  Greek  word  meaning  weak,  in  allusion 
to  its  weak  electric  power  when  heated  or  rubbed. 

Natrolite. 

Composition.     Na2Al2Si30io.2H20.    A  zeolite. 

Crystallization.  Orthorhombic.  Crystals  usually  slender 
prismatic,  often  acicular.  Prism  zone  vertically  striated.  Some- 
times terminated  by  low  pyramid.  Crystals  often  appear  to 
be  tetragonal  in  symmetry.  Sometimes  in  cruciform  twins. 


MICA  GROUP  271 

Structure.  Usually  in  radiating  crystal  groups  (see  Fig.  C, 
pi.  II) ;  also  fibrous,  massive,  granular  or  compact. 

Physical  Properties.  Perfect  prismatic  cleavage.  H.  =  5-5.5. 
G.  =  2.25.  Vitreous  luster.  Colorless  or  white.  Sometimes 
tinted  yellow  to  red.  Transparent  to  translucent. 

Tests.  Easily  fusible  (2.5)  to  a  clear,  transparent  glass  giving 
a  yellow  (sodium)  flame.  Water  in  C.  T.  Soluble  in  hydro- 
chloric acid  and  gelatinizes  upon  evaporation.  Recognized 
chiefly  by  its  radiating  crystals. 

Occurrence.  A  mineral  of  secondary  origin,  found  lining  amygda- 
loidal  cavities  in  basalt,  etc.  Associated  with  other  zeolites,  calcite, 
etc.  Notable  localities  for  its  occurrence  are  Aussig  and  Teplitz, 
Bohemia;  Puy  de  Dome,  France;  Fassathal,  Tyrol;  Kapnik,  Hun- 
gary; in  various  places  in  Nova  Scotia;  Bergen  Hill,  New  Jersey; 
copper  district,  Lake  Superior. 

Scolecite. 

A  zeolite  with  composition  CaAl2Si3Oio.3H2O.  Monoclinic.  In 
slender  prismatic,  twinned  crystals.  In  radiating  groups.  Some- 
times fibrous.  Prismatic  cleavage.  H.  =  5-5.5.  G.  =  2.16-2.4. 
Vitreous  luster;  silky  when  fibrous.  Colorless  or  white.  Trans- 
parent to  almost  opaque.  Fuses  at  2.5  to  a  voluminous  frothy  slag. 
Gelatinizes  in  acids.  Water  in  C.  T.  A  mineral  of  secondary  origin, 
found  lining  cavities  in  basic  igneous  rocks,  associated  with  other 
zeolites,  etc. 

Thomsonite. 

A  zeolite,  having  the  composition  (Na2Ca)Al2(SiO4)2.2|H2O. 
Orthorhombic  but  distinct  crystals  rare.  Commonly  columnar 
with  radiated  structure.  Perfect  pinacoidal  cleavage.  H.  =  5-5.5. 
G.  =  2.3-2.4.  Vitreous  luster.  Colorless,  white,  gray.  Transparent 
to  translucent.  Fuses  with  intumescence  at  2-2.5.  Soluble  and 
gelatinizes  in  acids.  Much  water  in  C.  T.  Occurs  in  amygdaloidal 
cavities  in  basalt,  etc.,  associated  with  other  zeolites. 

MICA   DIVISION. 
MICA   GROUP. 

The  micas  form  a  series  of  complex  silicates  of  aluminium  with 
potassium  and  hydrogen,  also  often  magnesium,  ferrous  iron, 
and  in  some  varieties,  sodium,  lithium,  ferric  iron.  More  rarely 
manganese,  chromium,  barium,  fluorine  and  titanium  are  present 


272  MANUAL  OF  MINERALOGY 

in  small  amounts.  The  composition  of  many  of  the  micas  is 
not  definitely  understood  and  the  formulas  assigned  to  them 
are  only  approximate. 

They  crystallize  in  the  monoclinic  system  but  with  an  axial 
inclination  of  practically  90°,  so  that  their  monoclinic  sym- 
metry is  not  clearly  seen.  The  crystals  are  usually  tabular  with 
prominent  basal  planes,  and  have  either  a  diamond-  or  hexagonal- 
shaped  outline  with  angles  of  60°  and  120°.  The  crystals,  as  a 
rule,  therefore,  appear  to  be  either  orthorhombic  or  hexagonal 
in  their  symmetry.  They  are  all  characterized  by  a  very  perfect 
basal  cleavage. 

They  form  an  isomorphous  series,  and  various  gradations 
between  the  different  members  occur.  Their  isomorphism  is 
further  indicated  by  two  members  of  the  group  frequently 
crystallizing  together,  with  a  parallel  position,  in  the  same 
crystal  plate.  Biotite  occurs  crystallizing  in  this  way  with 
muscovite,  and  muscovite  with  lepidolite,  etc. 

The  important  members  of  the  group  follow: 

Muscovite,        H2KAl3(Si04)3. 
Lepidolite,        KLi[A1.2(OH,F)]Al(Si03)3. 
Biotite,  (H,K)2(Mg,Fe)2Al2(SiO4)3. 

Phlogopite,        H2KMg3Al(SiO4)3? 
Lepidomelane,  (H,K)2Fe3(Fe, Al)4(Si04)  5? 

Muscovite.     Common  Mica. 

Composition.  H2KAl3(Si04)3.  Contains  also  frequently  small 
amounts  of  ferrous  and  ferric  iron,  magnesium,  calcium,  sodium, 
lithium,  fluorine,  titanium,  etc. 

Crystallization.  Monoclinic  with  axial  angle  nearly  90°. 
Occurs  in  tabular  crystals  with  prominent  base.  The  pres- 
ence of  prism  faces  having  angles  of  60°  and  120°  with  each 
other  gives  the  plates  a  diamond-shaped  outline,  making  them 
simulate  orthorhombic  symmetry.  If  the  clinopinacoid  faces 
are  also  present,  the  crystals  become  hexagonal  in  outline  with 
apparently  hexagonal  symmetry.  The  prism  faces  are  roughened 
by  horizontal  striations  and  frequently  taper. 


MUSCOVITE  273 

Structure.  Foliated  in  large  to  small  sheets;- in  scales  which 
are  sometimes  aggregated  into  plumose  or  globular  forms.  Dis- 
tinct crystals  comparatively  rare. 

Physical  Properties.  Extremely  perfect  cleavage  parallel  to 
base,  allowing  the  mineral  to  be  split  into  excessively  thin  sheets. 
Folia  flexible  and  elastic.  H.  =  2-2.5.  G.  =  2.76-3.  Vitre- 
ous to  silky  or  pearly  luster.  Transparent  and  almost  colorless 
in  thin  sheets.  In  thicker  blocks,  opaque  with  light  shades  of 
brown  and  green.  May  be  yellow  to  white.  Some  crystals  are 
translucent  when  viewed  perpendicular  to  the  prism  zone  but 
opaque  in  a  direction  perpendicular  to  the  base. 

Tests.  Fusible  at  4.5-5.  Unattacked  by  boiling  hydro- 
chloric or  sulphuric  acids.  Characterized  by  its  micaceous 
structure  and  light  color.  Told  from  phlogopite  by  its  not  being 
decomposed  in  sulphuric  acid  and  from  lepidolite  by  not  giving 
a  crimson  flame  B.  B. 

Occurrence.  A  widespread  and  very  common  rock-making  min- 
eral. Found  in  such  igneous  rocks  as  granite  and  syenite.  Espe- 
cially characteristic  of  pegmatite  veins,  and  found  lining  cavities 
in  granites,  where  it  has  evidently  been  formed  by  the  action  of 
mineralizing  vapors  during  the  last  stages  of  the  formation  of  the 
rock.  Muscovite  is  chiefly  characteristic  of  the  deep-seated  igneous 
rocks,  and  is  not  found  in  the  recent  eruptive  rocks.  Also  very 
common  in  metamorphic  rocks,  as  gneiss  and  schist,  forming  the 
chief  constituent  in  certain  mica-schists.  In  some  schistose  rocks 
it  occurs  in  the  form  of  fibrous  aggregates  of  minute  scales  having  a 
silky  luster,  but  which  do  not  show  so  plainly  the  characters  of  the 
mineral.  This  variety  is  known  as  sericite,  and  is  usually  the  prod- 
uct of  alteration  of  feldspar.  Muscovite  also  originates,  as  the 
alteration  product  of  several  other  minerals,  as  topaz,  cyanite, 
spodumene,  adalusite,  scapolite,  etc.  Finite  is  a  name  given  to  the 
micaceous  alteration  product  of  various  minerals,  and  which  corre- 
sponds in  composition  more  or  less  closely  to  muscovite. 

In  the  pegmatite  veins,  muscovite  occurs  associated  with  quartz 
and  feldspar,  with  tourmaline,  beryl,  garnet,  apatite,  fluorite,  etc. 
It  is  found  often  in  these  veins  in  large  blocks,  which  are  at  times 
several  feet  across. 

Muscovite  is  found  in  the  United  States  in  commercial  deposits 
chiefly  in  the  Appalachian  and  Rocky  Mountain  regions.  The 
most  productive  pegmatite  veins  occur  in  North  Carolina,  mostly 
in  Mitchell,  Yancey,  Haywood,  Jackson  and  Macon  counties,  and 


274  MANUAL  OF  MINERALOGY 

in  the  Black  Hills  of  South  Dakota.  Of  less  importance  are  the 
deposits  in  Colorado,  Alabama  and  Virginia.  Muscovite  has  been 
mined  in  New  Hampshire,  Maine  and  Connecticut.  Large  deposits 
are  found  in  Canada  in  the  township  of  Grenville,  east  of  Ottawa, 
and  in  a  district  to  the  east  of  Quebec.  Large  and  important 
deposits  occur  in  India. 

Name.  Muscovite  was  so  called  from  the  popular  name  of  the 
mineral,  Muscovy-glass,  because  of  its  use  as  a  substitute  for 
glass  in  Russia.  Mica  was  probably  derived  from  the  Latin 
micare,  meaning  to  shine. 

Use.  Used  chiefly  as  an  insulating  material  in  the  manufac- 
ture of  electrical  apparatus.  Used  as  a  transparent  material 
(isinglass)  for  stove  doors,  lanterns,  etc.  Scrap  mica,  or  the 
waste  material  in  the  manufacture  of  sheet  mica,  is  used  in  many 
ways,  as  in  the  manufacture  of  wall  papers  to  give  them  a  shiny 
luster;  as  a  lubricant  when  mixed  with  oils;  as  a  nonconductor 
of  heat  and  as  a  fireproofing  material. 


Lepidolite. 

Composition.     Lithia  mica,  KLi[A1.2(OH.F)]Al(SiO8)3. 

Crystallization.  Monoclinic.  Crystals  usually  in  small 
plates  or  prisms  with  hexagonal  outline. 

Structure.  Commonly  in  coarse-  to  fine-grained  scaly  aggre- 
gates. 

Physical  Properties.  Perfect  basal  cleavage.  H.  =  2.5-4. 
G.  =  2.8.  Pearly  luster.  Color  pink  and  lilac  to  grayish  white. 
Translucent. 

Tests.  Easily  fusible  (2),  giving  a  crimson  flame  (lithium). 
Insoluble  in  acids.  Characterized  chiefly  by  its  micaceous 
structure  and  lilac  to  pink  color. 

Occurrence.  A  comparatively  rare  mineral,  found  in  pegmatite 
veins,  usually  associated  with  pink  and  green  tourmaline,  cassiterite, 
amblygonite,  spodumene,  etc.  Often  intergrown  with  muscovite  in 
parallel  position.  Notable  localities  for  its  occurrence  are  at  Roznau, 
Moravia;  St.  Michael's  Mount,  Cornwall;  western  Maine  at  Hebron, 
Auburn,  Norway,  Paris,  Rumford;  Chesterfield,  Massachusetts;  San 
Diego  County,  California. 


PHLOOOPITE  275 

Name.     Derived  from  a  Greek  word  meaning  scale. 
Use.     A  source  of  lithium  compounds. 

Biotite. 

Composition.     (H,K)2(Mg,Fe)2Al2(Si04)3. 

Crystallization.  Monoclinic.  In  tabular  or  short  prismatic 
crystals  with  prominent  basal  planes.  Crystals  rare,  frequently 
pseudorhombohedral. 

Structure.  Usually  in  irregular  foliated  masses;  often  in  dis- 
seminated scales  or  in  scaly  aggregates. 

Physical  Properties.  Perfect  basal  cleavage.  Folia  flexible 
and  elastic.  H.  =  2.5-3.  G.  =  2.95-3.  Splendent  luster.  Color 
usually  dark  green  and  brown  to  black.  More  rarely  lighter 
yellow.  Thin  sheets  usually  have  a  smoky  color  (differing  from 
the  almost  colorless  muscovite). 

Tests.  Difficultly  fusible  at  5.  Unattacked  by  hydrochloric 
acid.  Decomposed  by  boiling  concentrated  sulphuric  acid,  giv- 
ing a  milky  solution.  Characterized  by  its  micaceous  structure, 
cleavage  and  dark  color. 

Occurrence.  An  important  and  widely  distributed  rock-making 
mineral,  but  not  as  common  as  muscovite.  Occurs  in  igneous  rocks, 
especially  those  in  which  feldspar  is  prominent,  such  as  granite  and 
syenite.  Found  also  in  many  felsite  lavas  and  porphyries.  Less 
common  in  the  ferromagnesium  rocks.  Is  also  present  in  some 
metamorphosed  rocks,  as  gneiss  and  schist.  Occurs  in  fine  crystals 
in  the  lavas  of  Vesuvius. 

Phlogopite. 

Composition.  A  magnesium  mica,  near  biotite,  but  contain- 
ing no  iron,  H2KMg3Al(Si04)3(?).  Usually  contains  about  3  per 
cent  of  fluorine. 

Crystallization.  Monoclinic.  Usually  in  six-sided  plates  or 
in  tapering  prismatic  crystals.  Crystals  frequently  large  and 
coarse. 

Structure.     In  crystals  or  foliated  masses. 

Physical  Properties.  Perfect  basal  cleavage.  Folia  flexi- 
ble and  elastic.  H.  =  2.5-3.  G.  =  2.86.  Luster  vitreous  to 


276  MANUAL  OF  MINERALOGY 

pearly.  Color  yellowish  brown,  green,  white,  often  with  copper- 
like  reflections  from  the  cleavage  surface.  Transparent  in  thin 
sheets  to  opaque  in  the  mass. 

Tests.  Fusible  at  4.5-5.  Insoluble  in  hydrochloric  acid. 
Decomposed  by  boiling  concentrated  sulphuric  acid,  giving  a 
milky  solution.  Characterized  by  its  micaceous  structure,  cleav- 
age and  yellowish  brown  color.  Told  from  muscovite  by  its 
decomposition  in  sulphuric  acid  and  from  biotite  by  its  lighter 
color.  But  it  is  impossible  to  draw  a  sharp  distinction  between 
biotite  and  phlogopite. 

Occurrence.  Occurs  as  a  product  of  metamorphism  in  crystalline 
magnesium  limestones  or  dolomitic  marbles.  Rarely  found  in  ig- 
neous rocks.  Notable  localities  are  in  Finland;  Sweden;  Campo- 
longo,  Switzerland;  Ceylon,  etc.  In  North  America,  found  chiefly 
in  Jefferson  and  St.  Lawrence  counties,  New  York;  at  North  and 
South  Burgess,  Ontario,  and  in  various  localities  in  Quebec,  Canada. 

Name.     Named  from  a  Greek  word  meaning  firelike,  in  allu- 
sion to  its  color. 
Use.     Same  as  for  muscovite. 

Lepidomelane. 

A  mica,  that  may  be  regarded  as  a  variety  of  biotite,  characterized 
by  the  large  amount  of  ferric  iron  that  it  contains,  (H,K)2Fe3(Fe,Al)4- 
(SiO^sC?).  Monoclinic.  In  small  hexagonal-shaped  tables,  or  as 
an  aggregate  of  minute  scales.  Perfect  basal  cleavage.  H.  =  3. 
G.  =  3-3.2.  Adamantine  to  pearly  luster.  Color  black  to  green- 
ish black.  Opaque  or  translucent  in  very  thin  laminae.  Fuses  at 
4.5-5  to  a  magnetic  globule.  Decomposed  by  hydrochloric  acid. 
A  comparatively  rare  mineral,  found  chiefly  in  pegmatitic  granites 
and  syenites. 

CLINTONITE    GROUP. 

The  minerals  of  this  group  are  rare  species  that  lie  between 
the  true  micas  and  the  chlorites.  They  resemble  the  micas  in 
crystal  forms,  cleavage,  etc.,  but  differ  physically  in  that  their 
folia  are  brittle,  and  chemically  in  that  they  are  basic  in  char- 
acter. The  only  species  in  the  group  that  warrants  description 
is  margarite. 


CLINOCHLORE  277 


Margarite. 


A  micaceous  mineral  with  the  composition  H-jCaAhSiaO^.  Mono- 
clinic  but  seldom  in  distinct  crystals.  Usually  in  foliated  aggregates. 
Perfect  basal  cleavage.  H.  =  3.5-4.5  (harder  than  the  true  micas). 
G.  =  3.05.  Luster  vitreous  to  pearly.  Color  pink,  white  and  gray. 
Translucent.  Folia  somewhat  brittle.  Fuses  at  4-4.5.  Unat- 
tacked  by  acids.  Occurs  usually  with  corundum  and  apparently  as 
one  of  its  alteration  products.  Found  in  this  way  with  the  emery 
deposits  of  Asia  Minor;  on  the  islands  of  the  Greek  archipelago;  at 
Chester,  Massachusetts;  Chester  County,  Pennsylvania;  with  co- 
rundum deposits  in  North  Carolina,  etc. 

CHLORITE   GROUP. 

A  somewhat  ill-defined  group  of  closely  related  micaceous 
minerals  is  known  as  the  Chlorite  Group  or  as  the  chlorites. 
They  are  so  named  on  account  of  the  characteristic  green  color 
that  they  show.  They  are  silicates  of  aluminium  with  magne- 
sium, ferrous  iron  and  hydroxyl.  Ferric  iron  may  replace  the 
aluminium  in  small  amount.  Chromium  and  manganese  may 
occur.  Calcium  and  the  alkalies,  which  are  characteristic  of 
the  micas  proper,  are  practically  absent.  The  composition 
of  these  minerals  is  not  fully  understood.  Their  crystal  forms 
are  similar  to  those  of  the  micas  and  they  show  a  perfect  basal 
cleavage.  Their  laminae,  however,  are  tough  and  inelastic. 
Clinochlore  is  the  most  common  member  of  the  group. 

Clinochlore.     Penninite. 

Composition.     H8Mg5Al2SisOi8.     See  above. 

Crystallization.  Monoclinic.  In  six-sided  tabular  crystals, 
with  prominent  basal  planes.  Similar  in  habit  to  the  crystals 
of  the  mica  group,  but  distinct  crystals  rare.  Penninite  is 
pseudorhombohedral  in  symmetry,  otherwise  it  is  identical  with 
clinochlore. 

Structure.  Usually  foliated  massive  or  in  aggregates  of 
minute  scales;  in  finely  disseminated  particles;  earthy. 

Physical  Properties.  Perfect  basal  cleavage.  Folia  flexible 
but  not  elastic.  H.  =  2-2.5.  G.  =  2.65-2.75.  Vitreous  to 


278  MANUAL  OF  MINERALOGY 

pearly  luster.     Color  green  of  various  shades.     Rarely  pale 
green,  yellow,  white,  rose-red.     Transparent  to  opaque. 

Tests.  Difficultly  fusible,  5-5.5.  Unattacked  by  hydro- 
chloric acid.  Decomposed  by  boiling  concentrated  sulphuric 
acid,  giving  a  milky  solution.  Characterized  by  its  green  color, 
micaceous  structure  and  cleavage  and  by  the  fact  that  the  folia 
are  not  elastic. 

Occurrence.  A  common  and  widespread  mineral,  always  of  sec- 
ondary origin.  It  results  from  the  alteration  of  silicates  containing 
aluminium,  ferrous  iron  and  magnesium,  such  as  pyroxene,  amphi- 
bole,  biotite,  garnet,  vesuvianite,  etc.  To  be  found  where  rocks, 
containing  such  minerals,  are  undergoing  metamorphic  change. 
The  green  color  of  many  igneous  rocks  is  due  to  the  chlorite  into 
which  the  ferromagnesian  silicates  have  altered.  The  green  color  of 
many  schists  and  slates  is  due  to  finely  disseminated  particles  of  the 
mineral. 

Name.  Chlorite  is  derived  from  a  Greek  word  meaning  green, 
in  allusion  to  the  common  color  of  the  mineral. 

Serpentine. 

Composition.  A  magnesium  silicate,  H4Mg3Si209  =  Silica  44. 1 , 
magnesia  43.0,  water  12.9.  Ferrous  iron  and  nickel  may  be 
present  in  small  amount. 

Crystallization.  Monoclinic  (optically).  Occurs,  however, 
only  in  pseudomorphic  crystals. 

Structure.  Often  in  delicate  fibers,  which  can  be  separated 
from  each  other  (see  Fig.  D,  pi.  II).  Usually  massive,  but 
microscopically  fibrous  and  felted. 

Physical  Properties.  H.  =  2.5-5,  usually  4.  G.  =  2.5-2.65. 
Luster  greasy,  waxlike  in  the  massive  varieties,  silky  when 
fibrous.  Color  olive  to  blackish  green,  yellowish  green,  white. 
Color  often  variegated,  showing  mottling  in  lighter  and  darker 
shades  of  green.  Translucent  to  opaque. 

Tests.  Infusible.  Decomposed  by  hydrochloric  acid  with  the 
separation  of  silica  but  without  the  formation  of  a  jelly.  Fil- 
tered solution,  after  being  oxidized  with  nitric  acid  and  having 
any  iron  precipitated  by  ammonium  hydroxide,  and  the  absence 


SERPENTINE  279 

of  calcium  proved  by  addition  of  ammonium  oxalate,  gives  a 
precipitate  of  ammonium-magnesium  phosphate  with  sodium 
phosphate.  Water  in  C.  T.  Recognized  by  its  variegated  green 
color  and  its  greasy  luster  or  by  its  fibrous  structure. 

Varieties.  In  Crystals.  Occurs  in  crystals  as  pseudomorphs 
after  various  magnesian  silicates,  principally  chrysolite,  pyroxene, 
amphibole. 

Precious  Serpentine.  Massive,  translucent,  of  light  to 
dark  green  color.  Often  mixed  with  white  marble  and  shows 
beautiful  variegated  coloring.  Frequently  called  verd  antique 
marble. 

Ordinary  Serpentine.  Massive,  opaque,  of  various  shades  of 
green. 

Chrysotile.  The  fibrous  asbestiform  variety,  which  is  to  be 
found  in  veins  traversing  the  massive  serpentine.  This  is  the 
asbestos  of  commerce  for  the  most  part. 

Occurrence.  A  common  mineral  and  widely  distributed.  Always 
as  an  alteration  product  of  some  magnesian  silicate,  especially  chryso- 
lite, also  pyroxene,  amphibole,  etc.  Frequently  associated  with 
magnesite,  chrysolite,  chromite,  etc.  Found  in  both  igneous  and 
metamorphic  rocks,  sometimes  in  disseminated  particles,  sometimes 
in  such  quantity  as  to  make  up  practically  the  entire  rock-mass. 
Precious  serpentine  is  found  at  Falun  and  Gulsjo,  Sweden;  Isle  of 
Man;  Cornwall,  etc.  The  fibrous  variety,  chrysotile,  comes  from  the 
Province  of  Quebec,  Canada,  just  north  of  the  Vermont  line;  from 
Vermont;  New  York;  New  Jersey;  Grand  Canyon,  Arizona,  etc. 

Name.  The  name  refers  to  the  green  serpentlike  cloudings 
of  the  massive  variety. 

Use.  The  variety  chrysotile  is  the  chief  source  of  asbestos. 
Fibrous  amphibole  (which  see)  is  also  used  for  the  same  purposes. 
The  uses  of  asbestos  depend  upon  its  fibrous,  flexible  structure, 
which  allows  it  to  be  woven  into  cloth,  felt,  etc.,  and  upon 
its  incombustibility  and  slow  conductivity  of  heat.  Asbestos 
products,  therefore,  are  used  for  fireproofing  and  as  an  insulating 
material  against  heat  and  electricity.  The  massive  mineral  is 
often  used  as  an  ornamental  stone  and  may  at  times  be  valuable 
as  building  material. 


280  MANUAL  OF  MINERALOGY 


Genthite.     Garnierite. 

Nickel  silicates  of  uncertain  composition.  Genthite  contains  mag- 
nesium, Ni2Mg2Si3Oio.6H2O(?) ;  Garnierite,  H2NiSiO4(?) .  Amorphous, 
earthy  to  slightly  botryoidal  structure.  As  incrustations.  H.  = 
3-4.  G.  =  2.2-2.8.  Earthy  and  dull  luster.  Color  apple-green 
to  white.  Infusible.  Difficultly  decomposed  by  hydrochloric  acid, 
giving  separated  silica.  In  O.  F.  color  the  borax  bead  brown.  In 
C.  T.  blacken  and  give  water.  Genthite  found  with  chromite  at 
Texas,  Lancaster  County,  Pennsylvania.  Garnierite  occurs  in  con- 
siderable amount,  associated  with  serpentine  and  chromite,  near 
Noumea,  New  Caledonia,  and  serves  as  an  important  ore  of  nickel. 

Talc.     Steatite.     Soapstone. 

Composition.  A  magnesium  silicate,  H2Mg3(Si03)4  =  Silica 
63.5,  magnesia  31.7,  water  4.8. 

Crystallization.  Monoclinic.  Crystals  rare.  Usually  tabu- 
lar with  rhombic  or  hexagonal  outline. 

Structure.  Foliated  massive;  sometimes  in  radiating  foliated 
groups.  Also  compact. 

Physical  Properties.  Perfect  basal  cleavage.  Thin  folia 
somewhat  flexible  but  not  elastic.  Sectile.  H.  =  1  (will  make 
a  mark  on  cloth).  G.  =  2.8.  Pearly  to  greasy  luster.  Color 
apple-green,  gray,  white;  in  soapstone  often  dark  gray  or  green. 
Translucent  to  opaque.  Greasy  feel. 

Tests.  Difficultly  fusible  (5).  Unattacked  by  acids.  Char- 
acterized by  its  micaceous  structure  and  cleavage,  by  its  softness 
and  greasy  feel.  To  be  distinguished  from  pyrophyllite  by 
moistening  a  fragment  with  cobalt  nitrate  and  heating  intensely; 
talc  will  assume  a  pale  violet  color,  pyrophyllite  a  blue  color. 

Varieties.  Foliated  Talc.  Light  green  or  white,  foliated,  with 
a  greasy  feel. 

Steatite  or  Soapstone.  Massive,  with  fine  granular  to  crypto- 
crystalline  structure.  Gray  to  dark  green  colors;  often  impure, 
through  the  presence  of  such  minerals  as  chlorite,  tremolite, 
mica,  etc. 

Pseudomorphous.  Is  frequently  pseudomorphous  after  such 
minerals  as  enstatite,  pyroxene,  amphibole,  chrysolite,  etc. 


KAOLIN  281 

Occurrence.  Talc  is  a  mineral  of  secondary  origin  formed  by 
the  alteration  of  magnesium  silicates,  such  as  chrysolite,  enstatite, 
pyroxene,  amphibole,  etc.  Found  at  times  in  the  igneous  rocks, 
because  of  the  alteration  of  such  silicates,  especially  in  peridotites 
and  pyroxenites.  Most  characteristically  found,  however,  in  the 
metamorphic  rocks,  where  it  may  form  as  soapstone,  practically  the 
entire  rock-mass,  or  occur  as  a  prominent  constituent  in  the  schistose 
rocks,  as  in  talc-schist.  In  the  United  States,  talc  or  soapstone 
quarries  are  to  be  found  chiefly  along  the  line  of  the  Appalachian 
Mountains,  the  mineral  being  produced  in  Vermont,  Massachusetts, 
Rhode  Island,  New  York,  New  Jersey,  Pennsylvania,  Maryland, 
Virginia,  North  Carolina,  and  Georgia.  Important  deposits  are 
located  in  St.  Lawrence  County,  New  York,  where  the  talc  occurs 
in  the  form  of  beds  of  schist  interstratified  with  limestones.  It  is 
associated  here  with  tremolite  and  enstatite,  from  masses  of  which 
it  has  evidently  been  derived.  Large  deposits  of  soapstone  occur  in 
Virginia  in  a  narrow  belt  running  from  Nelson  County  northeast 
into  Albemarle  County.  It  occurs  here  in  sheets  sometimes  100  or 
more  feet  in  thickness.  There  is  a  long  series  of  talc  and  soapstone 
deposits  in  Vermont,  located  along  the  east  side  of  the  Green  Moun- 
tains. Talc  has  been  mined  in  considerable  quantity  in  Swain 
County,  North  Carolina. 

Use.  In  the  form  of  slabs,  soapstone  is  used  extensively  for 
wash  tubs,  sinks,  table  tops,  electrical  switchboards,  hearth- 
stones, furnace  linings,  etc.  An  especially  compact  variety  is 
used  for  the  tips  of  gas  burners,  for  tailors'  chalk,  slate  pencils, 
by  the  Chinese  for  carvings,  etc.  Talc  is  also  used  in  a  finely 
powdered  form  as  a  filler  to  give  weight  to  paper,  as  a  lubricant, 
for  toilet  powders,  in  paints,  as  a  heat  insulator,  etc. 


Kaolin  or  Kaolinite. 

Composition.  An  aluminium  silicate,  H4Al2Si209 = Silica  46.5, 
alumina  39.5,  water  14. 

Crystallization.  Monoclinic.  In  very  minute,  thin,  rhombic 
or  hexagonal-shaped  plates. 

Structure.  Usually  in  claylike  masses,  either  compact  or 
friable. 

Physical  Properties.  Perfect  basal  cleavage.  H.  =  2-2.5. 
G.  =  2.6-2.63.  Luster  usually  dull  earthy;  crystal  plates 


282  MANUAL  OF  MINERALOGY 

pearly.     Color  white.     Often  variously  colored  by  impurities. 
Usually  unctuous  and  plastic. 

Tests.  Infusible.  Insoluble.  Assumes  a  blue  color  when 
moistened  with  cobalt  nitrate  and  ignited  (aluminium).  Recog- 
nized usually  by  its  claylike  character. 

Occurrence.  Of  widespread  occurrence.  The  chief  constituent 
of  clay.  Always  a  mineral  of  secondary  origin,  being  derived  by  the 
alteration  of  aluminium  silicates,  particularly  feldspar.  It  is  found 
mixed  with  feldspar  in  rocks  that  are  undergoing  alteration;  at 
times  it  forms  entire  beds  where  such  alteration  has  been  carried  to 
completion.  As  one  of  the  common  products  of  the  decomposition 
of  rocks  it  gets  into  soils  and  being  transported  by  water  is  deposited, 
mixed  with  quartz  and  other  materials  in  lakes,  etc.,  in  the  form  of 
beds  of  clay. 

Name.  Kaolin  is  a  corruption  of  the  Chinese,  Kauling,  a 
locality  from  which  material  was  obtained  for  the  manufacture 
of  porcelain  and  which  was  thought  to  be  the  same  as  kaolin. 

Use.  Used  in  the  form  of  clay  in  making  all  kinds  of  pottery, 
stoneware,  bricks,  etc.  The  finer,  purer  grades  of  kaolin  are 
used  in  the  manufacture  of  porcelain,  china,  etc. 

Pyrophyllite. 

Composition.  H2Al2(Si03)4  =  Silica  66.7,  alumina  28.3,  water 
5.0. 

Crystallization.     Monoclinic  (?).     Not  observed  in  crystals. 

Structure.  Foliated,  sometimes  in  radiating  lamellar  aggre- 
gates. Also  granular  to  compact.  Identical  with  talc  in  struc- 
ture and  appearance. 

Physical  Properties.  Perfect  basal  cleavage.  Folia  some- 
what flexible  but  not  elastic.  H.  =  1-2  (will  make  a  mark  on 
cloth).  G.  =  2.8-2.9.  Pearly  to  greasy  luster.  Color  white, 
apple-green,  gray,  brown.  Usually  opaque.  Greasy  feel. 

Tests.  Infusible.  Unattacked  by  acids.  Characterized 
chiefly  by  its  micaceous  structure  and  cleavage,  its  softness  and 
greasy  feel.  Only  to  be  easily  distinguished  from  talc  by  mois- 
tening a  small  fragment  with  cobalt  nitrate  and  igniting,  when 
it  assumes  a  blue  color  (aluminium).  Talc  under  the  same 
conditions  would  become  pale  violet. 


TITANITE  283 

Occurrence.  A  comparatively  rare  species.  Found  in  meta- 
morphic  rocks;  frequently  with  cyanite.  Occurs  in  considerable 
amount  in  Moore  and  Chatham  counties,  North  Carolina. 

Use.  Quarried  in  North  Carolina  and  used  for  the  same  pur- 
poses as  talc.  It  does  not  command,  however,  as  high  a  price 
as  the  best  grades  of  talc.  A  considerable  part  of  the  so-called 
agalmatolite,  from  which  the  Chinese  carve  small  images,  is 
this  species. 

Chrysocolla. 

Composition.  Hydrous  copper  silicate,  CuSi03.2H20  =  Silica 
34.3,  copper  oxide  45.2,  water  20.5.  Varies  considerably  in  com- 
position and  often  impure. 

Structure.  Noncrystalline.  Massive  compact.  Sometimes 
earthy. 

Physical  Properties.  H.  =  2-4.  G.  =  2.0-2.4.  Luster  vit- 
reous to  earthy.  Color  green  to  greenish  blue;  brown  to  black 
when  impure. 

Tests.  Infusible.  Decomposed  by  hydrochloric  acid  with 
the  separation  of  silica  but  without  the  formation  of  a  jelly. 
Gives  a  copper  globule  when  fused  with  sodium  carbonate  on 
charcoal.  In  C.  T.  darkens  and  gives  water. 

Occurrence.  A  comparatively  rare  mineral  occurring  in  the 
oxidized  zones  of  copper  veins.  Associated  with  malachite,  azurite, 
cuprite,  native  copper,  etc.  Found  in  the  copper  districts  of  Arizona 
and  New  Mexico. 

Name.  Chrysocolla,  derived  from  two  Greek  words  meaning 
gold  and  glue,  which  was  the  name  of  a  similar  appearing  mate- 
rial used  to  solder  gold. 

Use.    A  minor  ore  of  copper. 

Titanite.     Sphene. 

Composition.  Calcium  titano-silicate,  CaTiSi06 = Silica  30.6, 
titanium  oxide  40.8,  lime  28.6.  Iron  is  usually  present  in  small 
amounts. 

Crystallization.  Monoclinic.  Crystals  varied  in  habit. 
Often  with  prominent  basal  plane  which  is  steeply  inclined  and 


284 


MANUAL  OF  MINERALOGY 


which  in  combination  with  short  prism  and  pyramid  faces 
a  thin  wedge-shaped  crystal  (Figs.  342  and  343). 


Fig.  342. 


Fig.  343. 


Structure.     Usually  crystallized  or  lamellar. 

Physical  Properties.  Prismatic  cleavage.  H.  =  5-5.5.  G.= 
3.4-3.55.  Resinous  to  adamantine  luster.  Color  gray,  brown, 
green,  yellow,  black.  Transparent  to  opaque. 

Tests.  Fusible  at  4  with  slight  intumescence  to  a  dark  mass. 
Only  slightly  attacked  by  hydrochloric  acid.  Fused  with  sodium 
carbonate;  fusion  dissolved  in  hydrochloric  acid;  the  solution 
when  boiled  with  tin  gives  a  violet  color  (titanium). 

Occurrence.  A  rather  common  accessory  mineral  in  igneous  rocks, 
being  found  as  small  crystals  in  granites,  diorites,  syenites,  trachytes, 
phonolites,  etc.  Also  found  often  in  crystals  of  considerable  size 
embedded  in  the  metamorphic  rocks,  gneiss,  chlorite-schist  and 
crystalline  limestone.  Very  commonly  associated  with  chlorite. 
Also  found  with  iron  ores,  pyroxene,  amphibole,  scapolite,  zircon, 
apatite,  feldspar,  quartz,  etc.  Notable  localities  for  its  occurrence 
in  crystals  are  Tavetsch,  St.  Gothard,  etc.,  Switzerland;  Ala,  Pied- 
mont; Sandford,  Maine;  Gouverneur,  Diana,  Rossie,  Fine,  Pitcairn, 
Edenville,  Brewster,  etc.,  in  New  York;  in  various  places  in  Ontario, 
Canada. 

Name.     Sphene  comes  from  a  Greek  word  meaning  'wedge  in 
allusion  to  a  characteristic  development  of  the  crystals. 
Perovskite,  CaTi03,  is  a  rare  isometric  titanate. 

NIOBATES  —  TANTALATES. 

Columbite  —  Tantalite. 

Composition.  A  niobate  and  tantalate  of  ferrous  iron  and 
manganese  (Fe,Mn)(Nb,Ta)206  which  varies  in  composition  from 
the  niobate,  colwnbite  (Fe,Mn)Nb206,  to  the  tantalate,  tantalite 


COLUMBITE  —  TANTALITE 


285 


Fig.  344. 


Also 


(Fe,Mn)Ta206.  Often  contains  small  amounts  of  tin,  tungsten, 
etc.  A  variety,  known  as  manganotantalite,  is  essentially  a 
tantalite  with  most  of  the  iron  re- 
placed by  manganese. 

Crystallization.  Orthorhombic. 
Habit  of  crystals  is  short  prismatic; 
often  in  square  prisms  because  of 
prominent  development  of  the  verti- 
cal pinacoids.  Terminated  by  basal 
plane,  pyramids  and  domes;  fre- 
quently complex  (Fig.  344).  At 
times  in  heart-shaped  contact  twins. 

Structure.     Crystallized  and  in  parallel  crystal  groups. 
frequently  granular  massive. 

Physical  Properties.  H.  =  6.  G.  =  5.3-7.3,  varying  with 
the  composition,  increasing  with  rise  in  percentage  of  tantalum 
oxide  present.  Submetallic  luster.  Color  iron-black,  frequently 
iridescent.  Streak  dark  red  to  black. 

Tests.  Difficultly  fusible  (5-5.5).  Fused  with  borax;  the 
bead  dissolved  in  hydrochloric  acid;  the  solution  boiled  with 
tin  gives  a  blue  color  (niobium).  There  is  no  simple  test  for 
tantalum.  Generally  when  fused  in  0.  F.  with  sodium  car- 
bonate gives  an  opaque  bluish  green  bead.  Fused  with  sodium 
carbonate  on  charcoal  in  R.  F.  yields  a  magnetic  mass.  Recog- 
nized usually  by  its  black  color,  submetallic  streak  and  high 
specific  gravity. 

Occurrence.  Occurs  in  granite  rocks  and  in  pegmatite  veins, 
associated  with  quartz,  feldspar,  mica,  tourmaline,  beryl,  spodu- 
mene,  cassiterite,  samarskite,  wolframite,  microlite,  monazite,  etc. 
Notable  localities  for  its  occurrence  are  the  west  coast  of  Greenland  ; 
Bodenmais,  Bavaria;  llmen  Mountains,  Siberia;  Western  Australia 
(manganotantalite);  Standish,  Maine;  Haddam,  Middletown  and 
Branchville,  Connecticut;  in  Amelia  County,  Virginia;  Mitchell 
County,  North  Carolina;  Black  Hills,  South  Dakota;  near  Canon 
City,  Colorado. 

Name.  The  two  names  are  derived  from  the  acid  elements 
that  the  minerals  contain.  Niobium  is  often  called  columbium. 


286  MANUAL  OF  MINERALOGY 

Use.  Source  of  tantalum,  which  is  used  in  making  filaments 
for  incandescent  electric  lamps.  It  is  said  that  more  than 
20,000  20-candle-power  electric-light  filaments  can  be  made 
from  one  pound  of  tantalum.  The  tantalum,  used  for  this  pur- 
pose in  the  United  States,  is  imported  and  is  derived,  chiefly, 
from  the  manganotantalite  deposits  of  western  Australia. 

There  are  a  number  of  other  niobates  and  tantalates,  all  of 
which  are  rare  in  occurrence.  The  following,  however,  might 
be  mentioned :  pyrochlore,  chiefly  a  niobate  of  the  cerium  metals 
and  calcium;  microlite,  essentially  Ca2Ta207;  fergusonite,  a  nio- 
bate of  yttrium,  erbium,  cerium,  uranium,  etc.;  samarskite,  a 
niobate  and  tantalate  of  ferrous  iron,  uranium  and  the  cerium 
metals. 

PHOSPHATES,   ETC. 

The  phosphates  and  the  related  arsenates,  vanadates  and 
antimonates  may  be  divided  into  three  classes:  (1)  Anhydrous 
Phosphates,  etc.;  (2)  Acid  and  Basic  Phosphates,  etc.;  (3)  Hydrous 
Phosphates,  etc. 

1.  ANHYDROUS  PHOSPHATES,   ETC. 
Xenotime. 

Yttrium  phosphate,  YPO4  Erbium  may  be  present  in  consider- 
able amount,  also  small  amounts  of  cerium,  silicon  and  thorium. 
Tetragonal.  Crystal  forms  resemble  those  of  zircon.  In  rolled 
grains.  Prismatic  cleavage.  H.  =  4-5.  G.  =  4.55-5.1.  Vitreous 
to  resinous  luster.  Color  yellowish  to  reddish  brown.  Opaque. 
Infusible.  Tests  as  in  monazite,  which  see.  A  rare  mineral  which 
occurs,  like  monazite,  as  an  accessory  constituent  in  granite,  gneiss 
and  pegmatite  veins.  Found  as  rolled  grains  in  the  stream  sands, 
particularly  in  Brazil. 

Monazite. 

Composition.  A  phosphate  of  the  cerium  metals 
(Ce,La,Di)P04  with  usually  some  thorium  silicate,  ThSi04. 

Crystallization.  Monoclinic.  Crystals  usually  small,  often 
flattened  parallel  to  the  orthopinacoid. 

Structure.  Usually  in  granular  masses,  frequently  as  sand. 
Crystals  rare. 


TRIPHYLITE  —  LITHIOPHILITE  287 

Physical  Properties.  H.  =  5-5.5.  G.  =  5.2-5.3.  Resinous 
luster.  Color  yellowish  to  reddish  brown.  Translucent  to 
opaque. 

•  Tests.  Infusible.  Insoluble  in  hydrochloric  acid.  After  fusion 
with  sodium  carbonate,  dissolve  in  nitric  acid  and  add  solution  to 
excess  of  ammonium  molybdate  solution.  A  yellow  precipitate 
forms  (test  for  a  phosphate) .  Decomposed  by  heating  with  con- 
centrated sulphuric  acid;  solution  after  dilution  with  water  and 
filtering  gives  with  ammonium  oxalate  a  precipitate  of  the  oxa- 
lates  of  the  rare  earths. 

Occurrence.  A  comparatively  rare  mineral  occurring  as  an  acces- 
sory mineral  in  gneissoid  rocks,  and  as  rolled  grains  in  the  sands 
derived  from  the  decomposition  of  such  rocks,  where  it  has  been 
preserved  because  of  its  hardness  and  high  specific  gravity.  Found 
in  the  United  States,  chiefly  in  North  and  South  Carolina,  both  in 
gneiss  and  in  the  stream  sands.  The  bulk  of  the  world's  supply  of 
monazite  sand  comes  from  the  provinces  of  Minas  .Geraes,  Rio  de 
Janeiro,  Bahia,  and  Sao  Paulo,  Brazil. 

Name.  The  name  monazite  is  derived  from  a  Greek  word 
meaning  to  be  solitary,  in  allusion  to  the  rarity  of  the  mineral. 

Use.  Monazite  is  the  chief  source  of  thorium  oxide,  which  it 
contains  in  amounts  varying  from  1  to  20  per  cent;  commercial 
monazite  usually  containing  between  3  and  9  per  cent.  Thorium 
oxide  is  used  in  the  manufacture  of  mantles  for  incandescent  gas 
lights. 

Triphylite  —  Lithiophilite. 

Phosphates  of  lithium  with  ferrous  iron  and  manganese.  Tri- 
phylite corresponds  to  LiFePO4,  Lithiophilite  to  LiMnPO4.  The 
two  molecules  are  isomorphous  and  replace  each  other  in  varying 
amounts.  Orthorhombic,  crystals  rare.  Commonly  massive,  cleav- 
able  to  compact.  Cleavage  parallel  to  base  and  brachypinacoid. 
H.  =  4.5-5.  G.  =  3.42-3.56.  Luster  vitreous  to  resinous.  Color 
bluish  gray  in  triphylite  to  salmon-pink  or  clove-brown  in  lithio- 
philite.  Translucent.  Fusible  at  2.5,  giving  red  lithium  flame. 
Triphylite  becomes  magnetic  on  heating  in  R.  F.  Lithiophilite  gives 
in  O.  F.  an  opaque  bluish  green  bead  with  sodium  carbonate.  Sol- 
uble in  nitric  acid  and  when  the  solution  is  added  to  an  excess  of  a 
solution  of  ammonium  molybdate  gives  yellow  precipitate  (test  for 
phosphoric  acid).  Rare  minerals  occurring  in  pegmatite  veins  asso- 
ciated with  other  phosphates,  etc.  Triphylite  found  at  Huntington, 


288 


MANUAL  OF  MINERALOGY 


Massachusetts;  Peru,  Maine;  Grafton,  New  Hampshire;  Raben- 
stein,  Bavaria;  Keityo,  Finland.  Lithiophilite  found  at  Branch ville, 
Connecticut. 

THE   APATITE   GROUP. 

The  Apatite  Group  consists  of  a  closely  related  series  of  min- 
erals crystallizing  in  the  pyramidal  group  of  the  hexagonal 
system.  They  are: 

Apatite,        .    Ca4(CaF)(P04)3. 

Pyromorphite,  Pb4(PbCl)(P04)3. 

Mimetite,         Pb4(PbCl)  (As04)3. 

Vanadinite,      Pb4(PbCl)  (V04)3. 

Apatite. 

Composition.  Fluor-apatite,  Ca4(CaF)(P04)3;  more  rarely 
chlor-apatite,  Ca^CaClXPOOs. 

Crystallization.  Hexagonal;  tri-pyramidal.  Crystals  usually 
long  prismatic  in  habit;  sometimes  short  prismatic  or  tabular. 


Usually  terminated  by  prominent  pyramid  of  first  order  and 
frequently,  a  basal  plane  (Figs.  345  and  346).  Some  crystals 
show  faces  of  the  third  order  pyramid  and  have  at  times  a  very 
complex  development. 

Structure.  Usually  crystallized;  also  granular  massive  to 
compact. 

Physical  Properties.  H.  =  5  (can  just  be  scratched  by  a 
knife).  G.  =  3.15.  Vitreous  to  subresinous  luster.  Color 
usually  some  shade  of  green  or  brown;  also  blue,  violet,  colorless. 
Transparent  to  opaque. 


APATITE  289 

Tests.  Difficultly  fusible  (5-5.5).  Soluble  in  acids.  Gives  a 
yellow  precipitate  of  ammonium  phosphomolybdate  when  dilute 
nitric  acid  solution  is  added  to  large  excess  of  ammonium  molyb- 
date  solution.  Concentrated  hydrochloric  acid  solution  gives 
white  precipitate  of  calcium  sulphate  when  a  few  drops  of  sul- 
phuric acid  are  added.  Recognized  usually  by  its  crystals,  color 
and  hardness.  Distinguished  from  beryl  by  the  prominent 
pyramidal  terminations  of  its  crystals  and  by  its  being  softer 
than  a  knife. 

Variety.  Phosphorite.  An  impure  variety  of  apatite  is  known 
as  phosphorite.  It  occurs  in  a  compact  or  earthy  form  or  in 
concretionary  and  nodular  masses  in  fossiliferous  rocks  of  different 
ages.  Probably  of  organic  origin. 

Occurrence.  Apatite  is  widely  disseminated  as  an  accessory  con- 
stituent in  all  classes  of  rocks;  igneous,  metamorphic  and  sedimen- 
tary. It  is  also  found  in  pegmatite  and  other  veins,  probably  of 
pneumatolytic  origin.  Found  in  titaniferous  magnetites.  Occa- 
sionally concentrated  into  large  deposits  or  veins.  In  the  form  of 
phosphorite  or  phosphate  rock  occurs  extensively  as  a  rock  strata. 

Apatite,  as  it  exists  scattered  in  small  crystals  throughout  the 
rocks,  slowly  undergoes  alteration  and  is  gradually  dissolved  by 
percolating  carbonated  waters.  Some  of  the  phosphoric  acid  thus 
brought  into  solution  goes  into  the  sea  where  it  is  absorbed  by  living 
organisms ;  some  remains  in  the  soil,  where  its  presence  is  a  necessary 
condition  for  fertility  and  from  which  it  is  absorbed  by  plants  and 
through  them  goes  into  the  bodies  of  animals.  The  large  bodies  of 
phosphorite  are  derived  from  organic  sources,  such  as  animal  remains. 
Bone  is  calcium  phosphate  in  composition. 

Apatite  occurs  in  commercial  amount  in  Ontario  and  Quebec, 
Canada.  It  is  found  there  in  crystals  and  masses  enclosed  in  crys- 
talline calcite  and  in  veins  and  irregular  nests  along  the  contact  of 
the  limestone  with  eruptive  rocks.  The  chief  deposits  lie  in  Ottawa 
County,  Quebec.  Crystalline  apatite  occurs  in  large  amounts  along 
the  southern  coast  of  Norway,  between  Langesund  and  Arendal. 
It  is  found  there  in  veins  and  pockets  associated  with  a  mass  of 
gabbro.  Nodular  deposits  of  phosphate  rock  are  found  at  intervals 
all  along  the  Atlantic  coast  from  North  Carolina  to  Florida,  the 
chief  deposits  being  in  the  latter  state.  High  grade  phosphate 
deposits  are  found  in  western  middle  Tennessee.  Commercial  de- 
posits of  phosphorite  are  to  be  found  in  northern  Wales,  in  northern 
France,  northern  Germany,  Belgium,  Spain,  etc. 


290  MANUAL  OF  MINERALOGY 

Finely  crystallized  apatite  occurs  at  various  localities  in  the  Alps; 
in  Alexander  County,  North  Carolina;  at  Auburn,  Maine,  etc. 

Use.  Apatite  and  phosphate  rock  are  chiefly  used  for  fer- 
tilizer purposes.  They  are  usually  ground  and  treated  with 
sulphuric  acid  to  render  the  phosphoric  acid  more  soluble. 
Transparent  varieties  of  apatite  of  fine  color  are  occasionally 
used  for  gem  material.  The  mineral  is  too  soft,  however,  to 
allow  of  its  very  extensive  use  for  this  purpose. 

Pyromorphite. 

Composition.  Pb4(PbCl)  (P04)3  =  Phosphorus  pentoxide  15.7, 
lead  protoxide  82.2,  chlorine  2.6.  The  phosphorus  is  often  re- 
placed by  arsenic  and  the  species  graduates  into  mimetite. 

Crystallization.     Hexagonal;  tri-pyramidal.     Prismatic  crys- 
^^^^SSpS^N    tals   with    basal   plane.      Rarely   shows 
pyramid  truncations.     Often  in  rounded 
barrel-shaped  forms.     Sometimes  cavern- 
ous, the    crystals    being  hollow  prisms 
(Fig.  328).    Frequently  in  parallel  groups. 
Structure.   Crystallized,  globular,  reni- 
.^.j  form,  fibrous  and  granular. 
/      Physical    Properties.       H.  =  3.5-4. 
G.  =  6.5-7.1.     Resinous   luster.     Color 
Fig.  347.  usually  various  shades  of  green,  brown, 

yellow;  more  rarely  orange-yellow,  gray,  white.     Subtransparent 
to  nearly  opaque. 

Tests.  Easily  fusible  (2).  Gives  a  lead  globule  when  fused 
on  charcoal  with  sodium  carbonate.  When  fused  alone  on  char- 
coal gives  a  globule  which  on  cooling  shows  crystalline  structure. 
Faint  white  sublimate  of  lead  chloride  when  heated  in  C.  T. 
A  few  drops  of  the  nitric  acid  solution  added  to  ammonium 
molybdate  solution  gives  a  yellow  precipitate  of  ammonium 
phosphomolybdate. 

Occurrence.'  A  mineral  formed  by  secondary  action  and  found 
in  the  upper  oxidized  portions  of  lead  veins,  associated  with  other 
lead  minerals.  Notable  localities  for  its  occurrence  are  the  lead 
mines  of  Poullaouen,  Brittany;  at  Ems  in  Nassau;  in  the  Nerchinsk 


VANADINITE  291 

district,  Siberia;  Cornwall;  Phoenix ville,  Pennsylvania;  Davidson 
County,  North  Carolina,  etc. 

Name.  Derived  from  two  Greek  words  meaning  fire  said  form 
in  allusion  to  the  crystalline  form  it  assumes  on  cooling  from 
fusion. 

Use.    A  subordinate  ore  of  lead. 

Mimetite. 

Composition.  Pb4(PbCl)(As04)3  =  Arsenic  pentoxide  23.2, 
lead  protoxide  74.9,  chlorine  2.4.  Phosphorus  replaces  the 
arsenic  in  part  and  calcium,  the  lead.  Endlichite  is  a  variety 
intermediate  between  mimetite  and  vanadinite. 

Crystallization.  Hexagonal;  tri-pyramidal.  Crystals  pris- 
matic, showing  basal  plane  and  at  times  pyramids.  Usually  in 
rounded  barrel-  to  globular-shaped  forms. 

Structure.     In  rounded  crystals,  mammillary  crusts. 

Physical  Properties.  H.  =  3.5.  G.  =  7-7.2.  Resinous  lus- 
ter. Colorless,  yellow,  orange,  brown.  Subtransparent  to  al- 
most opaque. 

Tests.  Easily  fusible  (1.5).  Gives  globule  of  lead  when 
fused  with  sodium  carbonate  on  charcoal.  A  fragment  placed 
in  C.  T.  and  heated  in  contact  with  a  splinter  of  charcoal  gives 
deposit  of  metallic  arsenic  on  walls  of  tube. 

Occurrence.  A  comparatively  rare  mineral  of  secondary  origin, 
occurring  in  the  upper,  oxidized  portion  of  lead  veins.  Notable 
localities  for  its  occurrence  are  in  Cornwall,  Devonshire,  and  Cum- 
berland, England ;  Johanngeorgenstadt,  Saxony;  Nerchinsk,  Siberia; 
Pho3nixville,  Pennsylvania;  Cerro  Gordo,  California,  etc. 

Name.     Derived  from  the  Greek  for  imitator  in  allusion  to  its 
resemblance  to  pyromorphite. 
Use.    A  minor  ore  of  lead. 

Vanadinite. 

Composition.  Pb4(PbCl)(V04)3  =  Vanadium  pentoxide  19.4, 
lead  protoxide  78.7,  chlorine  2.5.  Phosphorus  and  arsenic  some- 
times present  in  small  amount  replacing  vanadium.  In  the 
variety  endlichite  the  proportion  of  V206  to  As206  is  nearly  as  1 : 1. 


292  MANUAL  OF  MINERALOGY 

Crystallization.  Hexagonal;  tri-pyramidal.  Prism  with  base. 
Sometimes  small  pyramidal  faces,  rarely  the  pyramid  of  the 
third  order.  In  rounded  crystals;  sometimes  cavernous. 

Structure.    In  crystals  and  globular  forms.    As  incrustations. 

Physical  Properties.  H.  =  3.  G.  =  6.9-7.1.  Adamantine 
to  resinous  luster.  Color  ruby-red,  brown,  yellow.  Transparent 
to  opaque. 

Tests.  Easily  fusible  (1.5).  Gives  globule  of  lead  on  charcoal 
when  fused  with  sodium  carbonate.  Gives  an  amber  color  in 
0.  F.  to  salt  of  phosphorus  bead  (vanadium).  Dilute  nitric  acid 
solution  gives  with  silver  nitrate  a  white  precipitate  of  silver 
chloride.  Endlichite  would  give  in  C.  T.  the  reaction  for  arsenic 
(see  under  mimetite). 

Occurrence.  A  rare  mineral  of  secondary  origin  found  in  the 
upper  oxidized  portion  of  lead  veins.  Occurs  in  various  districts  in 
Arizona  and  New  Mexico. 

Use.  Source  of  vanadium  and  minor  ore  of  lead.  Vanadium 
is  obtained  chiefly  from  other  ores,  such  as  the  sulphide,  patron- 
ite;  the  vanadate,  carnotite;  and  a  vanadium  mica,  roscoelite. 
Vanadium  is  used  chiefly  as  a  steel  hardening  metal.  Meta- 
vanadic  acid,  HV03,  is  used  as  a  yellow  pigment,  known  as 
vanadium  bronze.  Vanadium  oxide  is  used  as  a  mordant  in 
dyeing. 


Amblygonite. 

A  phosphate  of  lithium  and  aluminium,  Li(AlF)PC>4,  having 
hydroxyl  isomorphous  with  the  fluorine  and  often  sodium  in  small 
amount  replacing  the  lithium.  Triclinic.  Usually  massive,  cleav- 
able  to  compact.  Perfect  basal  cleavage.  H.  =6.  G.  =  3.08. 
Luster  vitreous,  pearly  on  cleavage  face.  Color  white  to  pale 
green  or  blue.  Translucent.  Easily  fusible  (2)  giving  a  red  flame 
(lithium).  Insoluble  in  acids.  After  fusion  with  sodium  carbonate 
and  dissolving  in  nitric  acid,  solution  with  excess  of  ammonium 
molybdate  solution  gives  yellow  precipitate  (test  for  phosphate).  A 
rare  mineral  found  in  pegmatite  veins  with  tourmaline,  lepidolite, 
apatite,  etc.  Found  at  Montebras,  France;  Hebron,  Paris,  Auburn, 
and  Peru,  Maine,  etc. 


SCORODITE  293 

2.  ACID  AND  BASIC  PHOSPHATES,  ETC. 
Olivenite. 

An  arsenate  and  hydroxide  of  copper,  Cu3As2O8.Cu(OH)2.  Ortho- 
rhombic.  Prismatic,  often  in  acicular  crystals.  Also  reniform, 
fibrous,  granular.  H.  =3.  G.  =  4.1-4.4..  Fusible  at  2-2.5.  Ada- 
mantine to  vitreous  luster.  Color  olive-green  to  blackish  green; 
also  shades  of  brown  and  yellow  to  white.  Translucent  to  opaque. 
With  sodium  carbonate  on  charcoal  gives  a  copper  globule.  When 
ignited  in  C.  T.  with  splinter  of  charcoal  gives  arsenical  mirror.  A 
little  water  when  heated  in  C.  T.  Found  rarely  in  oxidized  portions 
of  copper  veins. 

Lazulite. 

A  phosphate  of  magnesium  and  aluminium,  Mg(Al.OH)2(PO4)2, 
with  varying  amounts  of  ferrous  iron,  replacing  the  magnesium. 
Monoclinic,  usually  in  steep  pyramids.  Also  massive,  granular  to 
compact.  H.  =  5-5.5.  G.  =  3.05-3.1.  Vitreous  luster.  Azure- 
blue  color.  Translucent  to  opaque.  Infusible.  B.  B.  swells,  loses 
its  color  and  falls  to  pieces.  Insoluble.  A  rare  mineral. 

3.   HYDROUS  PHOSPHATES,   ETC. 
Vivianite. 

Hydrous  ferrous  phosphate,  Fe3P2O8.8H20.  Monoclinic.  Pris- 
matic crystals,  vertically  striated;  often  in  radiating  groups;  at 
times  fibrous  or  earthy.  Perfect  pinacoidal  cleavage.  H.  =  1.5-2. 
G.  =  2.58-2.68.  Vitreous  to  pearly  luster.  Colorless  when  un- 
altered. Blue  to  green  when  altered.  Transparent  when  fresh  to 
opaque  on  exposure.  Fusible  at  2-2.5  to  a  magnetic  globule. 
Nitric  acid  solution  added  to  an  excess  of  ammonium  molybdate 
solution  gives  yellow  precipitate  (test  for  phosphate).  Water  in 
C.  T.  A  rare  mineral  of  secondary  origin,  associated  with  pyrrho- 
tite,  pyrite,  limonite  and  other  iron  minerals. 

Erythrite  or  Cobalt  Bloom,  Co3As2Os.8H2O,  is  a  rare  secondary 
mineral  which  occurs  as  an  alteration  product  of  cobalt  arsenides. 
It  is  usually  pulverulent  in  structure  and  crimson  to  pink  in  color. 
Annabergite  or  Nickel  Bloom,  Ni3As2O8.8H2O,  is  a  similar  nickel 
compound.  It  is  light  green  in  color. 

Scorodite. 

A  hydrous  ferric  arsenate,  FeAsO4.2H20.  Orthorhombic, 
usually  in  pyramidal  crystals,  resembling  octahedrons;  also  pris- 
matic. Crystals  in  irregular  groups.  Also  earthy.  H.  =  3.5-4. 


294  MANUAL  OF  MINERALOGY 

G.  =  3.1-3.3.  Vitreous  luster.  Pale  green  to  liver-brown  in  color. 
Translucent.  Fusible  at  2-2.5.  Magnetic  when  heated  in  R.  F. 
Heated  intensely  with  splinter  of  charcoal  in  C.  T.  gives  arsenical 
mirror.  Water  in  C.  T.  In  hydrochloric  acid  reacts  for  ferric  iron. 
Occurs  in  oxidized  portions  of  metallic  veins  with  arsenopynte  and 
other  iron  minerals 

Wavellite. 

A  hydrous  aluminium  phosphate,  (A1OH)3(PO4)2-5H2O.  Ortho- 
rhombic,  crystals  rare.  Usually  in  radiating  globular  aggregates. 
Good  cleavage.  H.  =  3-4.  G.  =  2.33.  Vitreous  luster.  Color 
white,  yellow,  green  and  brown.  Translucent  Infusible.  In- 
soluble. Decomposed  by  fusion  with  sodium  carbonate  and  dis- 
solved in  nitric  acid  gives  yellow  precipitate  (test  for  phosphoric 
acid)  when  solution  is  added  to  excess  of  ammonium  molybdate. 
Moistened  with  cobalt  nitrate,  and  then  ignited  assumes  a  blue  color 
(aluminium).  A  rare  mineral. 

Turquois. 

Composition.  A  hydrous  phosphate  of  aluminium,  colored 
by  small  amounts  of  a  copper  phosphate,  H(A1.20H)2P04  with 
isomorphous  H(Cu.OH)2P04. 

Structure.  Noncrystalline.  Massive  compact,  reniform, 
stalactitic,  encrusting.  In  thin  seams  and  disseminated  grains. 

Physical  Properties.  H.  =  6.  G.  =  2.6-2.8.  Waxlike  lus- 
ter. Color  blue,  bluish  green,  green.  Translucent  to  opaque. 

Tests.  Infusible.  Insoluble.  After  fusion  with  sodium  car- 
bonate and  dissolving  in  nitric  acid,  gives  a  yellow  precipitate 
with  an  excess  of  ammonium  molybdate  solution  (test  for  a 
phosphate).  Gives  a  momentary  green  flame.  In  C.  T.  turns 
dark  and  gives  water. 

Occurrence.  Turquois  is  usually  found  in  the  form  of  small 
veins  and  stringers  traversing  more  or  less  decomposed  igneous 
rocks.  The  famous  Persian  deposits  are  found  in  trachyte  near 
Nishapur  in  the  province  of  Khorassan.  In  the  United  States  it 
is  found  in  much  altered  granite  or  granite  porphyry  in  Mohave 
County,  Arizona,  and  in  Grant  and  Santa  Fe  counties,  New  Mexico. 
Turquois  has  also  been  found  in  Nevada,  California  and  Colorado. 

Name.  Is  French  and  means  Turkish,  the  original  stones 
having  come  into  Europe  through  Turkey. 


NITER  295 

Use.  As  a  gem  stone.  It  is  always  cut  in  round  or  oval  forms 
and  a  one-carat  stone  may  be  valued  as  high  as  $10.  Much 
turquois  is  cut  which  is  veined  with  the  various  gangue  materials 
and  such  stones  are  sold  under  the  name  of  turquois  matrix. 

NITRATES. 
Soda  Niter. 

Composition.  Sodium  nitrate,  NaN03=  Nitrogen  pentoxide 
63.5,  soda  36.5. 

Crystallization.  Hexagonal-rhombohedral.  Homceomor- 
phous  with  calcite.  Has  closely  the  same  crystal  constants, 
cleavage,  optical  properties,  etc.,  as  calcite.  If  a  cleavage  block 
of  calcite  is  placed  in  a  crystallizing  solution  of  sodium  nitrate, 
small  rhombohedrons  of  the  latter  will  form  with  parallel  orien- 
tation on  the  calcite. 

Structure.     Usually  massive,  as  an  incrustation  or  in  beds. 

Physical  Properties.  Perfect  rhombohedral  cleavage.  H.  = 
1.5-2.  G.  =  2.29.  Vitreous  luster.  Colorless  or  white,  also 
reddish  brown,  gray,  yellow,  etc.  Transparent  to  opaque. 
Cooling  taste. 

Tests.  Very  easily  fusible  (1),  giving  a  strong  yellow  sodium 
flame.  After  intense  ignition  gives  an  alkaline  reaction  on 
moistened  test  paper.  Easily  and  completely  soluble  in  water. 
Heated  in  C.  T.  with  potassium  bisulphate  gives  off  red  vapors 
of  nitrous  oxide. 

Occurrence.  Because  of  its  solubility  in  water  it  is  only  to  be 
found  in  arid  and  desert  regions.  Found  in  large  quantities  in  the 
district  of  Tarapaca,  northern  Chile  and  the  neighboring  parts  of 
Bolivia.  Occurs  over  immense  areas  as  a  salt  (caliche)  bed  inter- 
stratified  with  sand,  beds  of  common  salt,  gypsum,  etc.  Has  been 
noted  in  Humboldt  County,  Nevada,  and  in  San  Bernardino  County, 
California. 

Use.  In  Chile  it  is  quarried,  purified  and  used  as  a  source  of 
nitrates. 

Niter. 

Potassium  nitrate,  KN03.  Orthorhombic.  Usually  as  thin  en- 
crustations or  as  silky  acicular  crystals.  Perfect  cleavage.  H.  =  2. 
G.  =  2.09-2.14.  Vitreous  luster.  Color  white.  Translucent. 


296  MANUAL  OF  MINERALOGY 

Easily  fusible  (1)  giving  violet  flame  (potassium).  After  ignition 
gives  alkaline  reaction  on  moistened  test  paper.  Heated  in  C.  T. 
with  potassium  bisulphate  gives  red  fumes  of  nitrous  oxide.  Easily 
soluble  in  water.  Saline  and  cooling  taste.  Found  as  delicate 
crusts,  as  an  efflorescence,  on  surfaces  of  earth,  walls,  rocks,  etc. 
Found  as  a  constituent  of  certain  soils.  Also  in  the  loose  soil  of 
limestone  caves.  Not  as  common  as  soda  niter,  but  produced  from 
soils  in  France,  Germany,  Sweden.  Obtained  in  India.  Used  'as  a 
source  of  nitrogen  compounds. 

BORAXES. 
Boracite. 

Composition,  Mg7Cl2Bi6O3o.  Isometric;  tetrahedral.  Crystals 
usually  show  cube,  tetrahedron  and  dodecahedron  in  some  com- 
bination. Crystals  usually  isolated  and  disseminated  in  other 
minerals.  Also  massive.  Vitreous  luster.  Colorless,  white,  gray, 
green.  Transparent  to  translucent.  H.  =7.  G.  =  2.9-3.0. 
Fusible  at  3  with  green  flame  color  (boron).  Soluble  in  hydrochloric 
acid.  Turmeric  paper  moistened  with  a  solution  of  the  mineral  and 
then  dried  at  100°  C.  turns  reddish  brown  (boron).  Occurs  asso- 
ciated with  halite,  anhydrite,  gypsum,  etc.,  as  one  of  the  products 
formed  by  the  evaporation  of  bodies  of  salt  water. 

Colemanite. 

Hydrous  borate  of  calcium,  Ca2B6Oii.5H2O.  Monoclinic,  in 
short  prismatic  crystals,  highly  modified.  Cleavable  massive  to 
granular  and  compact.  Perfect  pinacoidal  cleavage.  H.  =  4-4.5. 
G.  =  2.42.  Vitreous  to  adamantine  luster.  Colorless  to  white. 
Transparent  to  translucent.  Fusible  at  1.5.  B.  B.  exfoliates, 
crumbles  and  gives  green  flame  (boron).  Water  in  C.  T.  A  rare 
mineral,  but  occurring  in  considerable  quantity  in  the  salt  lake  de- 
posits, in  the  arid  regions  of  southeastern  California,  in  Death  Valley, 
Inyo  County,  and  in  San  Bernardino  and  Los  Angeles  counties. 

Borax. 

Composition.  Hydrous  sodium  borate,  Na2B407.10H20  = 
Boron  trioxide  36.6,  soda  16.2,  water  47.2. 

Crystallization.  Monoclinic.  Prismatic  crystals,  sometimes 
quite  large. 

Structure.  In  crystals  and  as  massive  cellular  material  or 
encrustations. 


URANINITE  297 

Physical  Properties.  Perfect  cleavage  parallel  to  orthopina- 
coid.  H.  =  2-2.5.  G.  =  1.75.  Vitreous  luster.  Colorless  or 
white.  Translucent  to  opaque.  Sweetish-alkaline  taste. 

Tests.  Easily  fusible  (1-1.5)  with  much  swelling  and  gives 
strong  yellow  flame  (sodium) .  Readily  soluble  in  water.  Tur- 
meric paper,  moistened  with  a  dilute  hydrochloric  acid  solution 
of  the  mineral,  turns  reddish  brown  when  dried  at.  100°  C. 
Much  water  in  C.  T. 

Occurrence.  Formed  as  a  deposit  from  the  evaporation  of  salt 
lakes,  and  as  an  efflorescence  on  the  surface  of  the  ground  in  arid 
regions.  The  deposits  in  Thibet  have  furnished  large  amounts  of 
borax,  which  has  been  exported  to  Europe  in  the  crude  state,  under 
the  name  of  tincal.  Found  in  quantity  in  the  United  States  in  the 
desert  region  of  southeastern  California,  in  Death  Valley,  Inyo 
County  and  in  San  Bernardino  County.  Occurs  also  in  the  adjacent 
parts  of  Nevada.  Borax  is  associated  with  the  other  minerals 
deposited  in  similar  manner,  such  as  halite,  gypsum,  colemanite,  and 
various  rare  borates. 

Name.     Borax  comes  from  an  Arabic  name  for  the  substance. 

Use.  Borax  is  used  for  washing  and  cleansing;  as  an  anti- 
septic, preservative,  etc.,  in  medicine;  as  a  solvent  for  metallic 
oxides  in  soldering  and  welding;  and  as  a  flux  in  various  smelt- 
ing and  laboratory  operations. 

URANATES. 
Uraninite.     Pitch  Blende. 

Composition.  An  uncertain  combination  of  the  oxides  of 
uranium,  U03  and  U02.  With  small  amounts  of  lead  and  the 
rare  elements,  thorium,  yttrium,  cerium,  nitrogen,  helium,  argon, 
radium.  It  is  the  mineral  in  which  the  gas  helium  was  first 
discovered  on  the  earth,  having  been  previously  noted  in  the 
gases  surrounding  the  sun  by  means  of  the  sun's  spectrum.  In 
it,  also,  was  first  discovered  the  rare  and  strange  substance, 
radium. 

Crystallization.  Isometric.  In  octahedrons,  also  with  do- 
decahedrons. Less  often  showing  cube  faces.  Crystals  rare. 

Structure.     Usually  massive  and  botryoidal;  also  in  grains. 


298  MANUAL  OF  MINERALOGY 

Physical  Properties.  H.  =  5.5.  G.  =  9-9.7  (unusually 
high).  Luster  submetallic  to  pitchlike,  dull.  Color  black. 
Streak  brownish  black. 

Tests.  Infusible.  Imparts  to  the  salt  of  phosphorus  bead 
in  0.  F.  a  yellowish  green  and  in  R.  F.  a  green  color.  Soluble 
in  dilute  sulphuric  acid  with  the  slight  evolution  of  helium  gas. 
Characterized  chiefly  by  its  pitchy  luster,  its  high  specific  gravity, 
its  color  and  streak. 

Occurrence.  Occurs  either  as  a  primary  constituent  of  granite 
rocks  or  as  a  secondary  mineral  with  ores  of  silver,  lead,  copper,  etc. 
Found  under  the  latter  condition  at  Johanngeorgenstadt,  Marienberg 
and  Schneeberg  in  Saxony,  at  Joachimsthal  and  Pfibram  in  Bohemia, 
and  Rezbdnya  in  Hungary.  Occurs  also  in  connection  with  the 
tin  deposits  of  Cornwall,  England.  In  the  United  States  found  in 
isolated  crystals  in  pegmatite  veins  at  Middletown,  Glastonbury 
and  Branchville,  Connecticut.  In  the  mica  mines  of  Mitchell 
County,  North  Carolina.  A  narrow  vein  of  it  has  been  mined 
near  Central  City,  Gilpin  County,  Colorado. 

Use.  The  chief  interest  in  the  mineral  lies  in  the  fact  that 
it  is  the  principal  source  of  radium.  This  element  exists  in  it 
in  extremely  small  percentages  and  it  is  necessary  to  subject  a 
large  amount  of  the  mineral  to  a  chemical  concentration  in  order 
to  produce  a  few  grains  of  a  radium  salt.  Uranium,  itself, 
has  only  a  limited  use.  Experiments  have  been  made  looking 
toward  its  use  in  steel.  In  the  form  of  various  compounds  it 
has  a  limited  use  in  coloring  glass  and  porcelain,  in  photography 
and  as  chemical  reagents. 

SULPHATES. 

The  sulphates  and  the  related  chromates  may  be  divided  into 
three  divisions:  (1)  Anhydrous  Sulphates;  (2)  Acid  and.  Basic 
Sulphates;  (3)  Hydrous  Sulphates. 

1.  ANHYDROUS  SULPHATES. 
Glaub  erite. 

A  sulphate  of  sodium  and  calcium,  Na2Ca(S04)2.  Monoclinic. 
Crystals  thin,  tabular  parallel  to  base.  Basal  cleavage.  H.  = 
2.5-3.  G.  =  2.7-2.85.  Vitreous  luster.  Color  pale  yellow  or  gray. 


BARITE  299 

Slightly  saline  taste.  Fusible  (1.5-2),  giving  yellow  flame  (sodium). 
After  ignition,  gives  an  alkaline  reaction  on  moistened  test  paper. 
Soluble  in  hydrochloric  acid  and  solution  with  barium  chloride  gives 
white  precipitate  of  barium  sulphate.  A  rare  mineral  occurring 
in  the  saline  deposits,  formed  by  the  evaporation  of  salt  lakes. 


BARITE   GROUP. 

The  Barite  Group  consists  of  the  sulphates  of  barium,  stron- 
tium, lead  and  calcium.  They  crystallize  in  the  orthorhombic 
system  with  closely  related  crystal  constants  and  similar  habits. 
The  members  of  the  group  are  as  follows : 

Barite,  BaS04. 
Cekstite,  SrS04. 
Anglesite,  PbS04. 
Anhydrite,  CaS04. 

Barite.     Barytes.     Heavy  Spar. 

Composition.  Barium  sulphate,  BaS04  =  Sulphur  trioxide 
34.3,  baryta  65.7.  Strontium  and  calcium  sulphates  present  at 
times. 


Fig.  348. 


Fig.  350. 


Fig.  352. 

Crystallization.  Orthorhombic.  Crystals  usually  tabular 
parallel  to  base;  often  diamond  shaped  because  of  the  presence 
of  a  short  prism  (Fig.  348).  Both  macro-  and  brachydomes 


300  MANUAL  OF  MINERALOGY 

usually  present,  either  beveling  the  corners  of  the  diamond- 
shaped  crystals  (Figs.  349  and  350),  or  if  the  prism  faces  are 
wanting,  beveling  the  edges  of  the  tables  and  forming  rectan- 
gular prismatic-shaped  crystals  elongated  parallel  to  either  the 
brachy-  or  macro-axis  (Figs.  351  and  352).  Crystals  sometimes 
quite  complex. 

Structure.  In  crystals.  In  divergent  groups  of  tabular  crys- 
tals forming  " crested  barite."  Also  coarsely  laminated;  granu- 
lar, earthy. 

Physical  Properties.  Perfect  cleavage  parallel  to  base  and 
prism  faces.  H.  =  3-3.5.  G.  =  4.5  (heavy  for  a  nonmetallic 
mineral).  Vitreous  luster;  pearly  at  times  on  base.  Colorless, 
white,  and  light  shades  of  blue,  yellow,  red.  Transparent  to 
opaque. 

Tests.  Fusible  at  4,  giving  yellowish  green  barium  flame. 
After  ignition  gives  an  alkaline  reaction  on  moistened  test  paper. 
Fused  with  sodium  carbonate  and  charcoal  dust  gives  a  residue, 
which,  when  moistened,  produces  a  dark  stain  of  silver  sulphide 
on  a  clean  silver  surface.  Recognized  by  its  white  color,  high 
specific  gravity,  characteristic  cleavage  and  crystals. 

Occurrence.  Barite  is  a  common  mineral  of  wide  distribution. 
It  occurs  usually  as  a  gangue  mineral  in  metallic  veins,  associated 
especially  with  ores  of  silver,  lead,  copper,  cobalt,  manganese  and 
antimony.  Sometimes  in  veins  in  limestone  with  calcite  and  celes- 
tite  or  in  sandstone  with  copper  ores.  At  times  acts  as  a  cement  in 
sandstone.  Deposited  occasionally  as  a  sinter  by  waters  from  hot 
springs.  Notable  localities  for  the  occurrence  of  crystalline  barite 
are  in  Westmorland,  Cornwall,  Cumberland,  Derbyshire,  and  Surrey, 
England;  Felsobanya  and  other  localities,  Hungary;  in  Saxony  and 
Bohemia.  In  the  United  States  at  Cheshire,  Connecticut;  De  Kalb, 
New  York;  Fort  Wallace,  New  Mexico.  Massive  barite,  occurring 
usually  as  veins,  nests  and  irregular  bodies  in  limestones,  has  been 
quarried  in  the  United  States  in  Connecticut,  Virginia,  North  Caro- 
lina, Georgia,  Tennessee,  Kentucky  and  Missouri. 

Use.  Barite  is  used  chiefly  for  the  production  of  barium 
hydroxide,  employed  in  the  refining  of  sugar.  It  is  ground 
and  used  as  a  white  pigment,  to  give  weight  to  cloth  and 
paper,  etc. 


CELESTITE 


301 


Celestite. 

Composition.  Strontium  sulphate,  SrS04  =  Sulphur  trioxide 
43.6,  strontia  56.4. 

Crystallization.  Orthorhombic.  Crystals  resemble  closely 
those  of  barite  (which  see).  Commonly  tabular  parallel  to  the 
base  or  prismatic  parallel  to  the  brachy-  or  macro-axis  with 
prominent  development  of  the  domes  (Fig.  353).  Crystals  which 
are  elongated  parallel  to  the  brachy-axis  are  frequently  termi- 
nated in  front  by  four  faces  in  nearly  equal  development,  con- 
sisting of  2  prism  faces  and  2  of  the  macrodome  (Fig.  354). 


Fig.  353. 


Fig.  354, 


Structure.  Crystallized.  Also  radiating  fibrous;  sometimes 
granular. 

Physical  Properties.  Perfect  cleavage  parallel  to  base  and 
prism.  H.  =  3-3.5.  G.  =  3.95-3.97.  Luster  vitreous  to  pearly. 
Colorless,  white,  often  faintly  blue  or  red.  Transparent  to 
translucent. 

Tests.  Fuses  at  3.5-4  and  colors  the  flame  crimson  (stron- 
tium). After  ignition  gives  an  alkaline  reaction  on  moistened 
test  paper.  Fused  with  sodium  carbonate  and  charcoal  dust 
gives  a  residue,  which,  when  moistened,  produces  on  a  clean 
silver  surface  a  dark  stain  of  silver  sulphide.  Closely  resembles 
barite  and  it  will  usually  need  a  flame  test  to  positively  differen- 
tiate the  two  species. 

Occurrence.  Celestite  is  found  usually  disseminated  through 
limestone  or  in  nests  and  lining  cavities  in  such  a  rock.  Associated 
with  calcite,  dolomite,  gypsum,  halite,  sulphur,  etc.  Notable 
localities  for  its  occurrence  are  with  the  sulphur  deposits  of  Sicily; 
at  Bex,  Switzerland;  Yate,  Gloucestershire,  England;  Herrengrund, 
Hungary;  Strontian  Island,  Put-in-Bay,  Lake  Erie,  Mineral 


302  MANUAL  OF  MINERALOGY 

County,  West  Virginia;  San  Bernardino  County,  California.  Found 
disseminated  in  limestones  near  Syracuse,  New  York,  and  in  Monroe 
County,  Michigan. 

Name.  Derived  from  ccdestis  in  allusion  to  the  faint  blue 
color  often  present. 

Use.  Used  in  the  preparation  of  nitrate  of  strontium  for 
fireworks.  Other  strontium  salts  used  in  the  refining  of  sugar. 

Anglesite. 

Composition.  Lead  sulphate,  PbS04  =  Sulphur  trioxide  26.4, 
lead  oxide  73.6. 

Crystallization.  Orthorhombic.  Crystal  habit  often  similar 
to  that  of  barite  (which  see)  but  much  more  varied.  Crystals 
may  be  prismatic  parallel  to  all  three  of  the  crystal  axes  and 
frequently  show  many  forms,  with  a  complex  development. 

Structure.  Crystallized.  Also  massive,  granular  to  compact. 
Frequently  earthy,  in  concentric  layers  about  a  nucleus  of 
galena. 

Physical  Properties.  Perfect  cleavage  parallel  to  base  and 
prism.  H.  =  2.75-3.  G.  =  6.12-6.39  (unusually  high).  Ada- 
mantine luster  when  pure  and  crystalline,  dull  when  earthy. 
Colorless,  white,  pale  shades  of  yellow,  green  and  blue.  May 
be  colored  dark  gray,  etc.,  by  impurities.  Transparent  to 
opaque. 

Tests.  Easily  fusible  at  2.5.  On  charcoal  with  sodium  car- 
bonate reduced  to  a  lead  globule  with  yellow  to  white  coating 
of  lead  oxide.  Fused  with  sodium  carbonate  and  charcoal  dust 
gives  a  residue,  which,  when  moistened,  produces  on  a  clean  silver 
surface  a  dark  stain  of  silver  sulphide.  Recognized  by  its  high 
specific  gravity,  its  adamantine  luster  and  frequently  by  its 
association  with  galena. 

Occurrence.  Anglesite  is  a  common  lead  mineral  of  secondary 
origin.  It  is  formed  through  the  oxidation  of  galena,  sometimes 
directly  to  the  sulphate  as  is  shown  by  the  concentric  layers  of  angle- 
site  found  at  times  surrounding  a  core  of  unaltered  galena,  or  some- 
times by  an  intermediate  solution  and  subsequent  recrystallization. 
Found  in  the  upper,  oxidized  portions  of  lead  veins,  associated  with 
galena,  cerussite,  sphalerite,  smithsonite,  calamine,  iron  oxides,  etc 


CROCOITE  303 

Notable  localities  for  its  occurrence  are  Monte  Poni,  Sardinia;  Is- 
land of  Anglesea,  England;  at  Leadhills,  Scotland;  various  localities 
in  Hungary,  etc.  Found  in  large  amounts  in  Australia.  Occurs  in 
the  United  States  at  Phoenix ville,  Pennsylvania;  Carroll  County, 
Maryland;  Colorado;  Cerro  Gordo,  California. 

Name.   Named  from  the  original  locality  on  Island  of  Anglesea. 
Use.     An  ore  of  lead. 

Anhydrite. 

Composition.  Anhydrous  calcium  sulphate,  CaS04  =  Sulphur 
trioxide  58.8,  lime  41.2. 

Crystallization.  Orthorhombic.  Crystals  rare;  when  ob- 
served are  thick  tabular,  also  prismatic  parallel  to  the  macro-axis. 

Structure.  Usually  in  crystalline  masses,  with  rectangular 
cleavage.  Fibrous,  granular. 

Physical  Properties.  Cleavage  parallel  to  the  three  pinacoids, 
so  yielding  rectangular  blocks.  H.  =  3-3.5.  G.  =  2.89-2.98. 
Luster  vitreous  to  pearly.  Color  white  with  sometimes  a  faint 
gray,  blue  or  red  tinge.  Transparent  to  translucent. 

Tests.  Fusible  at  3-3.5.  After  ignition  gives  an  alkaline 
reaction  on  moistened  test  paper.  Moistened  with  hydrochloric 
acid  and  ignited  gives  orange-red  flame  of  calcium.  Soluble  in 
hot  hydrochloric  acid  and  dilute  solution  with  barium  chloride 
gives  white  precipitate  of  barium  sulphate. 

Occurrence.  Occurs  in  much  the  same  manner  as  gypsum,  and 
often  associated  with  that  mineral  but  is  not  nearly  as  common. 
Found  in  beds  associated  with  salt  deposits  and  in  limestone  rocks. 
Found  at  times  in  amygdaloidal  cavities  in  basalt.  Occurs  at  Aussee 
in  Styria;  at  Stassfurt,  Prussia;  Bavaria;  Hall  in  Tyrol;  Bex, 
Switzerland;  in  the  United  States  at  Lockport,  New  York;  Nash- 
ville, Tennessee.  Found  in  large  beds  in  Nova  Scotia. 

Crocoite. 

Lead  chromate,  PbCrO4.  Monoclinic.  In  slender  prismatic  crys- 
tals, vertically  striated.  Also  granular.  H.  =  2.5-3.  G.  =  5.9- 
6.1.  Adamantine  luster.  Color  bright  red.  Orange-yellow  streak. 
Fusible  at  1.5.  Fused  with  sodium  carbonate  on  charcoal  gives  a 
lead  globule.  With  borax  gives  a  green  bead  in  O.  F.  A  rare 
mineral  found  in  the  oxidized  zones  of  lead  veins.  Fine  crystals 
come  from  Mount  Dundas,  Tasmania. 


304 


MANUAL  OF  MINERALOGY 


2.  ACID  AND  BASIC  SULPHATES. 
Brochantite. 

A  basic  sulphate  of  copper,  CuSO4 .  3  Cu(OH)2.  Orthorhombic. 
Slender  prismatic  crystals,  vertically  striated,  often  acicular.  Some- 
times massive  reniform.  Perfect  pinacoidal  cleavage.  H.  =  3.5-4. 
G.  =  3.9.  Vitreous  luster.  Emerald  to  blackish  green  in  color. 
Transparent  to  translucent.  Fusible  (3.5).  Copper  globule  when 
fused  with  sodium  carbonate  on  charcoal.  Hydrochloric  acid  solu- 
tion with  barium  chloride  gives  white  precipitate  of  barium  sul- 
phate. Water  in  C.  T.  A  rare  mineral  found  in  the  oxidized 
portions  of  copper  veins. 

3.   HYDROUS  SULPHATES. 

Gypsum.     Selenite. 

Composition.  Hydrous  calcium  sulphate,  CaS04.2H20  =  Sul- 
phur trioxide  46.6,  lime  32.5,  water  20.9. 

Crystallization.  Monoclinic.  Crystals  usually  tabular  paral- 
lel to  clinopinacoid;  in  diamond-shaped  crystals  with  edges 
beveled  by  prism  and  pyramid  faces  (Fig.  355).  Other  forms 
rare.  Sometimes  twinned  (Fig.  356). 


Fig.  355. 


Fig.  356. 


Structure.  Cleavable  massive;  foliated;  granular  massive; 
sometimes  with  fibrous  appearance. 

Physical  Properties.  Cleavage  in  three  directions;  perfect 
parallel  to  clinopinacoid,  yielding  easily  thin  folia;  with  con- 
choidal  surface  parallel  to  orthopinacoid;  with  fibrous  fracture 


GYPSUM  305 

parallel  to  a  pyramid.  H.  =  2  (can  be  scratched  by  the  finger 
nail).  G.  =  2.32.  Usually  with  vitreous  luster;  sometimes 
silky.  Colorless,  white,  gray;  sometimes  various  shades  of  yel- 
low, red,  brown,  etc.,  from  impurities.  Transparent  to  opaque. 

Tests.  Fusible  at  3-3.5.  After  intense  ignition,  residue  gives 
alkaline  reaction  on  moistened  test  paper.  Soluble  in  hot  dilute 
hydrochloric  acid  and  solution  with  barium  chloride  gives  white 
precipitate  of  barium  sulphate.  Much  water  in  C.  T.  Charac- 
terized by  its  softness  and  its  perfect  pinacoidal  cleavage. 

Varieties.     Crystalline,     In  crystals  or  foliated  masses. 

Fibrous.  With  coarse  to  fine  fibrous  appearance.  Satin  spar 
is  fine  fibrous  with  silky  luster. 

Massive.  Alabaster,  a  fine-grained  variety.  Rock  gypsum, 
massive  granular  or  earthy;  often  impure. 

Occurrence.  Gypsum  is  a  common  mineral  which  is  widely  dis- 
tributed in  sedimentary  rocks,  often  as  thick  beds.  It  frequently 
occurs  interstratified  with  limestones  and  shales.  Usually  to  be 
found  as  a  layer  underlying  beds  of  rock  salt  and  has  been  deposited 
there  as  one  of  the  first  minerals  to  crystallize  because  of  the  concen- 
tration of  salt  waters.  Occurs  also  as  lenticular  bodies  or  scattered 
crystals  in  clays  and  shales.  Found  at  times  in  volcanic  regions, 
especially  where  limestones  have  been  acted  upon  by  sulphur  vapors. 
Also,  is  common  as  a  gangue  mineral  in  metallic  veins.  Associated 
with  many  different  minerals,  the  more  common  ones  being  salt, 
anhydrite,  dolomite,  calcite,  sulphur,  pyrite,  quartz.  Deposits  of 
gypsum  of  commercial  importance  are  found  in  many  localities  in 
the  United  States,  but  the  chief  producers  are  located  in  New  York, 
Oklahoma,  Texas,  Iowa,  Michigan,  Ohio,  Virginia  and  Kansas. 
Gypsum  is  found  in  large  deposits  in  Arizona  and  New  Mexico  in  the 
form  of  wind-blown  sand. 

Name.  Derived  from  the  Greek  name  for  the  species.  At 
times  the  crystalline  variety  is  called  selenite,  which  comes  from 
a  Greek  word  meaning  moon,  probably  in  allusion  to  the  moon- 
like  white  reflections  from  some  varieties. 

Use.  Gypsum  is  chiefly  used  for  the  production  of  plaster  of 
Paris.  In  the  manufacture  of  this  material,  the  gypsum  is 
ground  and  then  heated,  until  a  large  proportion  of  the  water 
has  been  driven  off.  This  plaster,  when  mixed  with  water, 
slowly  absorbs  the  water  and  so  hardens  or  "sets."  Plaster  of 


306  MANUAL  OF  MINERALOGY 

Paris  is  used  extensively  for  " staff,"  the  material  from  which 
temporary  exposition  buildings  are  built,  and  for  molds  and 
casts  of  all  kinds.  Gypsum  is  employed  in  making  adamant 
plaster  for  interior  use.  Serves  as  land  plaster,  for  a  fertilizer. 
Satin  spar  and  alabaster  are  cut  and  polished  for  various  orna- 
mental purposes  but  are  restricted  in  their  uses  on  account  of 
their  softness. 

Chalcanthite.     Blue  Vitriol. 

Composition.  Hydrous  copper  sulphate,  CuS04.5H20  =  Sul- 
phur trioxide  32.1,  cupric  oxide  31.8,  water  36.1. 

Crystallization.  Triclinic.  Crystals  commonly  tabular  paral- 
lel to  a  pyramid  face. 

Structure.  Crystallized,  also  massive  in  stalactitic  and  reni- 
form  structure,  sometimes  with  fibrous  appearance. 

Physical  Properties.  H.  =  2.5.  G.  =  2.12-2.30.  Vitreous 
luster.  Color  deep  azure-blue.  Transparent  to  translucent. 
Metallic  taste. 

Tests.  Fusible  at  3.  Gives  copper  globule  when  fused  with 
sodium  carbonate  on  charcoal.  Soluble  in  water.  Dilute  hydro- 
chloric acid  solution  gives  with  barium  chloride  precipitate  of 
barium  sulphate.  Much  water  in  C.  T.  Characterized  by  its 
blue  color  and  its  solubility  in  water. 

Occurrence.  A  rare  mineral,  found  at  times  in  arid  regions  as  a 
secondary  mineral,  occurring  near  the  surface  in  copper  veins,  and 
derived  from  the  original  copper  sulphides  by  oxidation.  Often 
deposited  from  the  waters  in  copper  mines. 

Use.  A  minor  ore  of  copper.  The  artificial  blue  vitriol  is 
used  in  calico  printing,  in  galvanic  cells,  and  in  various  manu- 
facturing industries. 

Kalinite.     Potash  Alum. 

A  hydrous  sulphate  of  aluminium  and  potassium,  K^SCV 
A12(SO4)3.24H2O.  Isometric;  pyritohedral.  Usually  fibrous  or  mas- 
sive. H.  =  2-2.5.  G.=  1.75.  Vitreous  luster.  Colorless  to  white . 
Transparent  to  translucent.  Fuses  at  1  with  swelling  and  gives  a 
violet  flame  (potassium).  Easily  soluble  in  water.  Astringent  taste. 
Hydrochloric  acid  solution  with  barium  chloride  gives  a  white  pre- 
cipitate of  barium  sulphate,  and  with  ammonium  hydroxide  in 


WOLFRAMITE-H  UBNERITE  307 

excess  gives  white  precipitate  of  aluminium  hydroxide.  A  com- 
paratively rare  mineral,  which  usually  occurs  as  efflorescence  on 
clays  and  slates,  particularly  those  containing  disseminated  pyrite. 
Also  at  times  in  connection  with  sublimation  products  from  vol- 
canoes. 

TUNGSTATES,    MOLYBDATES. 
Wolframite-Hiibnerite. 

Composition.  Tungstates  of  ferrous  iron  and  manganese. 
Wolframite  (Fe,Mn)W04,  in  which  the  ratio  of  the  iron  to  the 
manganese  varies  from  9:1  to  2:3.  Hubnerite,  nearly  pure 
MnW04. 

Crystallization.  Monoclinic.  Crystals  commonly  tabular 
parallel  to  the  orthopinacoid,  giving  bladed  forms.  Prism  zone 
vertically  striated. 

Structure.  In  bladed,  lamellar  or  columnar  forms.  Massive 
granular. 

Physical  Properties.  Perfect  cleavage  parallel  to  clinopina- 
coid.  H.  =  5-5.5.  G.  =  7.2-7.5.  Submetallic  to  resinous  lus- 
ter. Color  black  in  wolframite  to  brown  in  hiibnerite.  Streak 
from  nearly  black  to  brown. 

Tests.  Fusible  (3-4).  Insoluble  in  acids.  Fused  with 
sodium  carbonate,  fusion  then  dissolved  in  hydrochloric  acid, 
tin  added  and  solution  boiled  gives  a  blue  color  (tungsten).  In 
O.  F.  with  sodium  carbonate  gives  bluish  green  bead  (manga- 
nese). Wolframite  when  fused  with  sodium  carbonate  in  R.  F. 
on  charcoal  gives  a  magnetic  mass. 

Occurrence.  Comparatively  rare  minerals,  found  usually  with 
cassiterite  and  associated  also  with  scheelite,  bismuth,  quartz,  pyrite, 
galena,  sphalerite,  etc.  Found  in  fine  crystals  from  Schlaggenwald, 
Bohemia,  and  in  the  various  tin  districts  of  Saxony  and  Cornwall. 
Wolframite  occurs  in  the  United  States  in  the  Black  Hills,  South 
Dakota;  Boulder  County,  Colorado;  Seward  Peninsula,  Alaska. 
Hubnerite  is  found  near  Butte,  Montana;  in  various  localities  in 
Nevada  and  Arizona. 

Use.  Chief  ores  of  tungsten.  Tungsten  is  used  as  a  harden- 
ing metal  in  the  manufacture  of  tool  steel.  Also  as  a  filament 
in  incandescent  electric  lights.  Sodium  tungstate  is  used  in 
fire-proofing  cloth  and  as  a  mordant  in  dyeing. 


308  MANUAL  OF  MINERALOGY 

Scheelite. 

Composition.  Calcium  tungstate,  CaW04  =  Tungsten  tri- 
oxide  80.6,  lime  19.4.  Molybdenum  is  usually  present,  replacing 
a  part  of  the  tungsten. 

Crystallization.    Tetragonal;  tri-pyramidal.    Crystals  usually 
simple   pyramids   of   first   order.     Closely   resemble   isometric 
octahedrons  in  angles  (Fig.  357).    Faces  of 
the  pyramid  of  third  order  are  small  and 
rare. 

Structure.     Massive  granular;  in  crys- 
tals. 

Physical  Properties.     Cleavage  parallel 
to  pyramid  of   first  order.      H.  =  4.5-5. 
G.  =  6.05  (unusually  high  for  a   mineral 
with  nonmetallic  luster) .     Vitreous  to  ada- 
mantine luster.    Color  white,  yellow,  green, 
brown.     Usually  translucent  to  opaque,  sometimes  transparent. 
Tests.     Difficultly  fusible  (5).    Decomposed  by  boiling  hydro- 
chloric acid  leaving  a  yellow  residue  of  tungstic  oxide,  which, 
when  tin  is  added  to  the  solution  and  boiling  continued,  turns 
first  blue  then  brown.     Recognized  by  its  high  specific  gravity 
and  the  test  for  tungsten. 

Occurrence.  Occurs  usually  with  quartz  in  crystalline  rocks 
associated  with  cassiterite,  topaz,  fluorite,  apatite,  molybdenite, 
wolframite,  etc.  Found  at  times  with  gold.  Occurs  in  connection 
with  the  tin  deposits  of  Bohemia,  Saxony  and  Cornwall;  in  quantity 
in  New  South  Wales  and  Queensland.  Found  in  the  United  States 
at  Trumbull,  Connecticut;  near  Randsburg,  San  Bernardino  County, 
California;  near  Browns,  Humboldt  County,  Nevada;  near  Dragoon, 
Cohise  County,  Arizona. 

Use.  A  subordinate  ore  of  tungsten,  wolframite  (which  see) 
furnishing  the  greater  amount.  Tungsten  is  used  chiefly  as  a 
steel-hardening  metal. 

Wulfenite. 

Composition.  Lead  molybdate,  PbMo04  =  Molybdenum  tri- 
oxide  39.3,  lead  oxide  60.7.  Calcium  sometimes  replaces  the 
lead. 


WULFENITE  309 

Crystallization.  Tetragonal;  tri-pyramidal.  Crystals  usually 
square  tabular  in  habit  with  prominent  base.  Sometimes  very 
thin.  Edges  of  tables  beveled  with  faces  of  low  second  order 
pyramid.  More  rarely  pyramidal  in  habit.  Pyramid  of  third 
order  in  small  faces  and  very  rare. 

Structure.     In  crystals;  also  massive  granular,  coarse  to  fine. 

Physical  Properties.  H.  =  4.5-5.  G.  =  6.05.  Vitreous  to 
adamantine  luster.  Color  yellow,  orange,  red,  gray,  white. 
White  streak.  Transparent  to  subtranslucent. 

Tests.  Easily  fusible  at  2.  Gives  a  lead  globule  when  fused 
with  sodium  carbonate  on  charcoal.  With  salt  of  phosphorus 
in  R.  F.  gives  green  bead;  in  0.  F.  yellowish  green  when  hot  to 
almost  colorless  when  cold.  If  powdered  mineral  is  moistened 
with  concentrated  sulphuric  acid  and  evaporated  almost  to  dry- 
ness  in  a  porcelain  crucible  the  residue  will  show  a  deep  blue 
color  on  cooling  (molybdenum). 

Occurrence.  Found  in  the  oxidized  portion  of  lead  veins  with 
other  ores  of  that  metal,  especially  vanadinite  and  pyromorphite. 
Found  in  the  United  States  in  a  number  of  places  in  Utah,  Nevada, 
Arizona  and  New  Mexico. 

Use.  An  ore  of  molybdenum.  Molybdenum  is  used  as  a 
steel-hardening  metal.  In  the  form  of  ammonium  molybdate 
it  is  used  as  a  chemical  reagent,  as  a  fireproofing  material  and 
as  a  disinfectant.  Molybdenum  used  also  to  color  leather  and 
rubber. 

LISTS    OF   MINERALS    ARRANGED    ACCORDING 
TO   ELEMENTS. 

In  the  following  section  are  given  lists  of  the  minerals  that  are 
of  commercial  importance  because  of  some  element  which  they 
contain.  All  of  the  minerals  that  could  serve  as  a  source  of 
any  particular  element  are  grouped  together,  their  relative 
importance  being  indicated  by  the  type  used  in  printing  their 
names.  The  order  in  which  the  minerals  are  given  in  each  list 
is  the  same  as  that  in  which  they  are  described  in  the  previous 
section  of  this  book.  The  different  elements  have  been  treated 
in  alphabetical  sequence  in  order  to  facilitate  ready  reference 


310  MANUAL  OF  MINERALOGY 

to  them.  Each  table  will  be  followed  by  a  brief  general  discus- 
sion of  the  occurrence  of  the  minerals  given  in  it  and  by  a  short 
statement  as  to  the  uses  of  the  element  derived  from  them. 

Aluminium. 

Cryolite,  Na3AlF6.  Bauxite,  A120(OH)4. 

Corundum,  A1203.  The  Feldspars,  KAlSi308,  NaAlSi308, 

CaAl2Si203,  etc. 
Gibbsite,  A1(OH),.  Kaolin,  H4Al2Si209. 

Aluminium  is  the  most  common  of  all  the  metals.  Unlike 
other  metals,  however,  its  occurrence,  with  the  exception  of  the 
fluorides,  is  restricted  to  minerals  containing  oxygen.  It  is  most 
abundantly  found  in  the  rock-making  silicates,  in  the  majority 
of  which  it  is  an  essential  constituent.  It  also  occurs  in  large 
amount  in  the  clays.  The  minerals  which  can  be  used  as  ores 
of  the  metal  are,  however,  few  in  number,  the  only  one  at  present 
of  importance  being  bauxite.  The  enormous  amounts  of  alu- 
minium contained  in  the  various  silicates  are  not  yet  available 
because  of  the  difficulty  and  expense  of  extraction. 

Bauxite  is  produced  in  the  United  States  chiefly  from  Arkan- 
sas, Alabama,  Georgia  and  Tennessee.  The  deposits  in  Arkan- 
sas are  found  in  Pulaski  and  Saline  counties.  They  have  an 
average  thickness  of  10  to  15  feet.  In  one  district  the  beds  lie 
directly  upon  a  body  of  kaolin,  which  in  turn  rests  upon  a  syenite 
rock-mass  and  it  is  probable  that  both  minerals  have  been 
derived  from  its  decomposition.  The  Alabama-Georgia  district 
extends  from  Jacksonville,  Alabama,  to  Carters ville,  Georgia. 
The  ore  occurs  as  pockets  or  lenses  in  a  clay  which  has  been 
derived  by  weathering  processes  from  a  dolomite  limestone. 
The  bauxite  is  either  pisolitic  or  clay-like  in  structure. 

Cryolite,  imported  from  Greenland,  has  been  used  as  an  ore 
of  aluminium  and  at  present  is  used  as  a  flux  in  the  electrolytic 
process  by  which  most  of  the  metal  is  obtained. 

The  usual  process  at  present  by  which  aluminium  is  extracted 
from  the  bauxite  ores  is  briefly  as  follows :  The  ore  is  heated  to 
low  redness  with  sodium  carbonate  forming  sodium  aluminate. 
This  compound  is  leached  out  by  water  and  by  passing  C02  gas 


ANTIMONY  311 

into  the  solution  the  aluminium  is  precipitated  as  the  hydroxide. 
The  latter  on  being  heated  is  converted  into  the  oxide  of  the 
metal.  The  pure  metal  is  prepared  from  this  oxide  by  an  elec- 
trolytic process  which  takes  place  in  a  bath  of  fused  cryolite. 
The  tank  in  which  the  reaction  takes  place  is  lined  with  carbon 
and  forms  the  cathode,  while  graphite  rods  suspended  in  the 
bath  serve  as  the  anode.  The  metal  collects  in  the  bottom  of 
the  tank. 

Aluminium  is  valuable  because  of  its  low  density  and  because 
it  is  not  easily  oxidized  or  corroded.  It  is  a  good  electrical  con- 
ductor and  to  some  extent  is  replacing  copper  used  for  that  pur- 
pose. It  is  used  in  many  alloys,  particularly  with  zinc,  copper 
and  nickel.  It  is  used  in  small  amounts  in  casting  steel  in  order 
to  take  up  any  oxygen  in  the  melt  and  also  to  prevent  porosity 
in  the  metal.  Aluminium  and  iron  oxide  are  mixed  in  a  finely 
divided  state  to  form  the  material  known  as  thermit.  When 
this  mixture  is  ignited  the  heat  of  the  combustion  of  the  alumin- 
ium is  so  great  that  it  can  be  used  in  welding  iron  and  steel. 
Sheets  and  tubes  and  castings  of  aluminium  are  used  wherever  a 
light  weight  metal  is  desired,  for  instance  in  the  manufacture  of 
certain  parts  of  automobiles.  Aluminium  is  used  in  the  manu- 
facture of  cooking  utensils,  as  a  substitute  for  lithographic  stones 
and  zinc  plates,  as  powder  in  the  manufacture  of  metallic  paints, 
etc.  It  is  used  also  in  the  form  of  salts,  chiefly  alum  and  alu- 
minium sulphate,  to  harden  paper,  in  the  purification  of  water, 
as  mordants  in  dyeing,  in  baking  powders,  in  medicine,  etc. 

Antimony. 

Native  Antimony,  Sb.  Stibnite,  Sb2S5. 

Antimony  occurs  in  a  considerable  number  of  minerals,  es- 
pecially those  belonging  to  the  series  known  as  the  sulpho-salts, 
which  are  largely  combinations  of  copper,  lead  or  silver  with 
antimony  and  sulphur.  These  minerals  are  mined,  however, 
for  the  other  metals  that  they  contain  and  any  antimony  that 
is  produced  from  them  is  in  the  nature  of  a  by-product.  Stib- 
nite is  practically  the  only  mineral  which  is  mined  for  its  anti- 
mony. This  mineral  has  been  found  in  the  United  States  in  a 


312  MANUAL  OF  MINERALOGY 

comparatively  few  deposits.  It  has  been  mined  on  a  small  scale 
in  California,  Nevada  and  Idaho.  The  greater  part  of  the 
antimony  produced  in  the  United  States  is  derived  from  anti- 
monial  lead  which  is  an  alloy  of  the  two  metals  derived  from 
the  smelting  of  lead  ores  that  contain  small  amounts  of  antimony 
minerals.  Considerable  amounts  of  antimony  and  antimony 
ores  are  imported,  chiefly  from  China,  France,  Italy,  Mexico 
and  Japan. 

Antimony  is  used  in  alloys,  such  as  type  metal  (lead,  antimony 
and  bismuth),  babbitt  or  anti-friction  metal  (antimony,  tin,  etc.), 
britannia  metal  (tin  with  antimony  and  copper),  etc.  Antimony 
oxide  is  used  as  a  pigment  and  in  the  glazing  of  enameled  ware. 
The  sulphide  is  used  in  fireworks,  in  safety  matches  and  in  per- 
cussion caps.  Other  compounds  are  used  in  medicine  and  for 
various  purposes  in  the  arts. 

Arsenic. 

Native  Arsenic,  As.  Realgar,  AsS. 

Orpiment,  As2S3.  Arsenopyrite,  FeAsS. 

Arsenic  in  minerals  ordinarily  plays  the  part  of  a  nonmetallic 
element,  similar  to  sulphur  in  its  chemical  relations.  It  forms 
three  classes  of  compounds,  the  arsenides,  the  sulpharsenites 
and  the  arsenates.  The  number  of  minerals  which  contain 
arsenic  is  considerable  but  only  a  few  can  be  considered  as  dis- 
tinctively arsenic  minerals.  Arsenopyrite  is  the  only  one  which 
at  present  serves  as  an  ore.  Most  of  the  arsenic  oxide  produced 
comes  as  a  by-product  in  the  smelting  of  arsenical  ores  for  copper, 
gold,  lead,  etc.  Large  amounts  of  the  oxide  are  obtained  from 
the  smelting  of  the  copper  ores  at  Butte,  Mont.,  the  mineral 
enargite,  CuaAsS^  being  its  chief  source.  The  oxide  is  also  pro- 
duced at  smelting  plants  in  Washington  and  Utah.  Arseno- 
pyrite has  been  mined  at  Brinton,  Virginia. 

Metallic  arsenic  is  used  in  some  alloys,  particularly  with  lead 
in  shot  metal.  Arsenic  is  chiefly  used,  however,  in  the  form  of 
white  arsenic,  or  arsenious  oxide.  This  is  employed  in  medicine, 
as  a  poison,  as  a  preservative,  in  making  Paris  green  (an  arsenate 
and  acetate  of  copper),  as  a  pigment,  in  glass  manufacture,  etc. 


CADMIUM  313 

Barium. 

Witherite,  BaC03.  Barite,  BaS04. 

Barite  is  the  chief  source  of  barium  compounds.  It  has  been 
mined  in  the  United  States  in  Missouri,  North  Carolina,  Georgia, 
Kentucky  and  Tennessee.  The  mineral  is  ground  and  sometimes 
purified  by  washing  and  then  used  as  a  partial  substitute  for 
white  lead  in  paint,  to  give  weight  to  paper  and  cloth,  etc. 
Barium  hydroxide  is  used  extensively  in  sugar  refining. 

Bismuth. 

Native  Bismuth,  Bi.  Bismuthinite,  Bi2S3. 

The  most  important  bismuth  mineral  is  the  native  metal. 
Bismuth  is  produced,  however,  mostly  as  a  by-product  in  the 
smelting  of  gold  and  silver  ores.  Only  a  comparatively  small 
amount  is  obtained  in  the  United  States,  chiefly  from  Colorado 
and  Utah. 

Bismuth  is  used  in  the  alloys  which  it  forms  with  lead,  tin  and 
cadmium.  These  fuse  at  low  temperatures  and  are  used  for 
safety  fuses,  safety  plugs,  etc.  Various  compounds  of  bismuth 
are  used  in  medicine  and  in  the  arts. 

Cadmium. 

Greenockite,  CdS. 

Greenockite  is  the  only  cadmium  mineral  of  importance  and 
this  is  very  rare  in  occurrence.  The  cadmium  of  commerce  is 
obtained  from  zinc  ores  that  carry  a  small  amount  of  the  metal. 
Practically  the  entire  output  of  cadmium  in  the  United  States 
comes  from  the  zinc  ores  of  the  Joplin  district,  Missouri,  which 
frequently  contain  some  0.3  per  cent  of  the  metal.  The  zinc 
ores  of  Silesia  have  for  a  long  time  been  a  prominent  source  of 
cadmium. 

Cadmium  is  used  in  various  alloys,  such  as  low-fusing  alloys, 
dental  amalgam,  metal  for  stereotype  plates,  etc.  The  metal  is 
used  with  silver  in  electroplating.  The  sulphide,  CdS,  is  known 
as  cadmium-yellow  and  is  used  extensively  as  a  pigment.  Vari- 
ous salts  of  cadmium  find  uses  in  the  arts. 


314  MANUAL  OF  MINERALOGY 

Chromium. 
Chromite,  FeCr04  with  MgCr04.        Crocoite,  PbCr04. 

Chromite,  or  chromic  iron  ore,  is  the  chief  source  of  chromium. 
Its  production  in  the  United  States  is  very  small,  coming  mostly 
from  Shasta  County,  California.  It  has  also  been  found  in  work- 
able deposits  in  Pennsylvania,  Maryland,  North  Carolina  and 
Wyoming.  Large  amounts  of  the  ore  are  imported  from  New 
Caledonia,  Greece  and  Canada. 

Chromium  is  used  as  a  steel-hardening  metal.  It  gives  to 
steel  a  superior  hardness  and  if  added  in  the  proper  proportion 
does  not  produce  brittleness.  The  mineral  chromite  is  made 
into  bricks  that  are  used  as  linings  for  metallurgical  furnaces. 
Various  red,  orange  and  green  pigments  and  dyes  are  made  from 
chromium  compounds.  Chromium  salts  are  used  as  mordants 
in  the  dyeing  and  printing  of  cloth.  Chromium  compounds  are 
useful  in  tanning  leather. 

Cobalt. 

Linnseite,  Co3S4.  Cobaltite,  CoSAs. 

Smaltite,  CoAs2. 

Cobalt  is  a  rare  element  which  is  usually  found  in  small 
amounts  associated  with  nickel  minerals.  Much  of  the  cobalt 
of  commerce  is  produced  from  other  ores  as  a  by-product.  The 
only  source  of  cobalt  at  present  in  the  United  States  is  from  the 
lead  ores  of  southeastern  Missouri,  where  it  occurs  sparingly  as 
the  mineral  linnseite.  The  metal  is  produced  from  a  cobaltif- 
erous  manganese  ore  found  in  New  Caledonia,  and  also  from 
the  silver  ores  of  Cobalt,  Canada. 

Cobalt  is  chiefly  used  in  the  form  of  the  oxide  as  a  blue  pig- 
ment in  making  glass  and  pottery. 

Copper. 

Native  Copper,  Cu.  Bornite,  Cu5FeS4. 

Chalcocite,  Cu2S.  Chalcopyrite,  CuFeS2. 

Stromeyerite,  CuAgS.  Tetrahedrite,  Cu8Sb2S7. 

Covellite,  CuS.  Tennantite,  Cu&As2S7. 


COPPER  315 

Enargite,  CusAsS4.  Chrysocolla,  CuSi03.2H20. 

Atacamite,  Cu2Cl(OH)3.  Olivenite,  Cu(CuOH)As04. 

Cuprite,  Cu20.  Brochantite,  Cu4(OH)6S04. 

Malachite,  Cu(OH)2.CuC03.     Chalcanthite,  CuS04.5H20. 

Azurite,  Cu(OH)2.2CuC03. 

Copper  is  a  common  and  widely  distributed  element.  It  is 
found  in  a  number  of  important  minerals  which  usually  occur 
in  veins.  Chalcopyrite  is  the  most  important  ore,  and  in  most 
cases  is  the  only  primary  copper  mineral  in  a  deposit.  The 
other  important  sulphides,  bornite  and  chalcocite,  are  usually, 
although  not  always,  the  results  of  secondary  enrichment. 
Solutions  that  have  leached  out  the  copper  content  of  the  upper 
portion  of  a  copper  vein  will  react  with  the  unoxidized  chalco- 
pyrite  farther  down  to  enrich  it  in  respect  to  the  amount  of  cop- 
per it  contains  and  convert  it  into  bornite  and  chalcocite.  In 
this  way  copper  veins  often  show  in  the  upper  part,  just  below 
the  oxidized  zone,  a  body  of  enriched  sulphides.  The  veins  at 
Butte,  Montana,  are  notable  examples  of  this.  This  enriched 
sulphide  zone  is  to  be  observed  in  general  when  the  copper  veins 
traverse  igneous  rocks.  When  they  lie  in  limestones  the  upper 
portion  of  the  vein  is  more  liable  to  be  characterized  by  the 
presence  of  the  oxidized  copper  ores,  native  copper,  cuprite, 
malachite,  azurite,  chrysocolla,  etc.  Pyrite  often  contains  small 
amounts  of  copper  and  when  it  occurs  in  large  bodies  becomes 
an  important  ore  of  the  metal. 

Copper  is  produced  in  from  fifteen  to  twenty  of  the  states  and 
territories  of  the  United  States.  A  brief  description  of  the  chief 
districts  in  the  more  productive  states  follows.  Alaska:  Three 
districts  of  importance  have  been  developed;  the  Ketchikan 
district  where  the  ores  are  contact  bodies,  and  are  composed 
chiefly  of  pyrrhotite,  magnetite,  pyrite  and  chalcopyrite;  Prince 
William  Sound  district  including  several  mines  on  Latouche 
Island;  Copper  River  district  where  immense  bodies  of  chal- 
cocite and  azurite  occur  in  limestone.  Arizona:  The  most  pro- 
ductive district  is  that  of  Bisbee  where  the  ore  bodies  replace 
limestone  and  are  closely  associated  with  intrusive  rocks.  The 
original  ores  were  chiefly  cupriferous  pyrite,  but  secondary  en- 


316  MANUAL  OF  MINERALOGY 

richment  has  extended  to  great  depths.  Near  the  surface  large 
bodies  of  oxidized  ores  were  found.  The  Jerome  district  has 
large  bodies  of  ore  lying  in  an  igneous  rock  which  through  shear- 
ing has  been  rendered  almost  schistose  in  structure.  The  ores 
at  present  are  largely  sulphides.  Clifton-Morenci  district  has 
its  ores  occurring  as  contact  deposits  lying  in  limestone  and 
shales  into  which  dikes  of  porphyry  have  been  intruded,  and  as 
disseminated  bodies  lying  in  the  porphyry  itself.  The  workable 
ores  are  those  which  have  undergone  secondary  enrichment,  and 
consist  of  both  carbonates  and  sulphides.  Globe  district  has 
deposits  that  occur  as  lenticular  replacement  bodies  in  limestone 
and  as  deposits  in  fissures  in  diabase.  Disseminated  bodies  also 
occur.  California:  The  chief  districts  lie  in  Shasta  County, 
where  the  ores  occur  as  replacement  bodies  along  shear  zones 
in  a  granite  porphyry.  Colorado:  Most  of  the  copper  from  this 
state  comes  as  a  by-product  in  the  smelting  of  gold  and  silver 
ores  and  is  derived  chiefly  from  Lake,  San  Juan,  Gilpin,  Chaffee 
and  Clear  Creek  counties.  Idaho:  The  greater  part  of  the  out- 
put comes  from  the  Co3ur  d'Alene  district.  The  deposit  con- 
sists of  disseminated  bornite,  chalcocite  and  chalcopyrite  in  beds 
of  quartzite.  Michigan:  This  state  was  for  a  long  period  the 
most  important  producer  in  the  country,  and  still  ranks  with 
the  leading  three.  The  ores  are  unique  in  that  they  consist 
wholly  of  native  copper.  They  occur  on  Keweenaw  Peninsula, 
the  rocks  of  which  consist  of  a  series  of  alternating  sandstone 
conglomerate  beds  and  basic  lava  flows,  all  inclined  at  a  steep 
angle  to  the  northwest.  The  copper  is  found  disseminated 
through  and  acting  as  a  cement  in  the  conglomerates,  and  in  less 
important  deposits  in  the  amygdaloidal  layers  of  the  lavas. 
Montana:  The  one  important  district,  and  for  a  number  of 
years  the  most  important  copper  district  in  the  world,  is  at 
Butte.  The  ores  occur  as  replacement  veins  in  a  granitic  rock. 
The  ores  have  been  very  greatly  enriched  by  secondary  action 
forming  at  times  very  large  sulphide  bodies.  The  important 
ore  minerals  are  chalcopyrite,  chalcocite  and  enargite.  Nevada: 
The  important  district  is  at  Ely,  where  the  sulphide  ores  occur 
as  disseminations  in  highly  altered  porphyry.  New  Mexico: 


GOLD  317 

The  Santa  Rita-Hanover  and  the  Burro  Mountain  districts  are 
the  chief  producers.  Tennessee:  The  chief  district  is  that  of 
Ducktown.  The  ores  occur  as  steeply  dipping  lenses  in  a  schist 
and  contain  chiefly  pyrrhotite,  pyrite  and  chalcopyrite.  Utah: 
The  Bingham  district  has  ores  which  are  closely  associated  with 
a  granitelike  rock  called  monzonite  which  is  intruded  into  a 
series  of  quartzites,  limestones  and  shales.  The  bodies  are 
either  contact  deposits  in  limestone  or  in  large  disseminated 
deposits  in  the  monzonite.  The  Tintic  district  has  ore  bodies 
occurring  as  contact  deposits,  replacements  in  limestone  and 
filling  fissures,  the  last  being  the  most  important.  The  Frisco 
district  has  ores  which  consist  of  pyrite  and  chalcopyrite  occur- 
ring disseminated  in  a  monzonite. 

Important  copper  deposits  outside  of  the  United  States  are 
at  Rio  Tin  to  in  Spain;  in  Australasia,  at  Mount  Lyell  in  Tas- 
mania, at  Wallaroo  and  Moontain,  South  Australia,  at  Mount 
Morgan  in  Queensland  and  at  different  localities  in  New  South 
Wales;  in  Mexico  at  Cananea  and  at  various  districts  in  Sonora, 
etc.;  in  Canada  at  the  Boundary  district  in  British  Columbia 
and  the  Sudbury  district  in  Ontario.  Chile,  Japan  and  Germany 
also  produce  notable  amounts  of  copper. 

Copper  is  extensively  used  in  the  form  of  wire,  sheet  and  nails. 
A  large  amount,  chiefly  as  wire,  is  used  as  an  electrical  conductor. 
It  has  important  uses  in  various  alloys,  as  brass  (copper  and 
zinc),  bronze  and  bell  metal  (copper  and  tin,  at  times  zinc  also), 
Gepman  silver  (copper,  zinc  and  nickel),  etc.  Copper  sulphate, 
or  blue  vitriol,  is  used  in  calico  printing  and  in  galvanic  cells. 

Gold. 

Native  Gold,  Au,  with  small  amounts  of  Ag. 
Petzite,  (Ag,Au)2Te.  Krennerite,  AuTe2. 

Sylvanite,  AuAgTe4.  Calaverite,  AuTe2. 

By  far  the  greater  part  of  gold  occurs  as  the  native  metal.  It 
enters  into  only  one  series  of  compounds,  the  tellurides,  and 
these  minerals,  while  at  times  forming  rich  ore  deposits,  as  at 
Cripple  Creek,  Colorado,  are  found  in  only  a  few  districts.  For 


318  MANUAL  OF  MINERALOGY 

the  occurrence  and  associations  of  the  gold  ores  see  under  gold, 
page  125;  under  calaverite,  page  158;  and  sylvanite,  page  157. 
The  uses  of  gold  for  jewelry,  plating  and  coins  are  well  known. 
The  standard  gold  for  United  States  coin  is  composed  of  9  parts 
gold  and  1  part  copper.  The  gold  used  in  jewelry  is  alloyed  with 
copper  and  silver  in  order  to  harden  it.  The  purity  of  gold  is 
given  in  carats;  24  carats  being  the  pure  metal.  Most  of  the 
gold  used  is  18  carats  fine  or  $f  gold  and  ^  other  metals.  Gold 
is  used  as  the  standard  of  international  exchange  and  one  troy 
ounce  is  worth  $20.67. 

Iron. 

Hematite,  Fe203.  Goethite,  Fe203(OH)2. 

Magnetite,  Fe304.  Limonite  Fe403(OH)6. 

Turgite,  Fe405(OH)2.  Siderite,  FeC03. 

Iron,  next  to  aluminium,  is  the  most  abundant  metal  in  the 
crust  of  the  earth.  It  very  rarely  occurs  native,  being  found 
chiefly  in  the  form  of  oxides,  sulphides  and  silicates.  It  is  found 
in  greater  or  less  amount  in  many  rocks,  especially  in  those  that 
contain  the  amphiboles,  pyroxenes,  micas  or  olivine.  The  min- 
eral species  that  contain  iron  are  very  numerous  but  the  minerals 
of  importance  as  ores  number  only  three  or  four.  Iron  occurs 
in  large  amounts  in  the  sulphides,  pyrite,  FeS2,  being  the  most 
common  of  all  sulphides.  These,  however,  never  serve  as  ores 
of  the  metal  because  of  the  injurious  effects  of  the  presence  of 
sulphur  upon  the  iron.  The  minerals  used  as  ores  are  'the 
various  oxides  or  the  carbonate. 

The  various  iron  ores  are  formed  under  different  conditions, 
and  as  a  rule  occur  alone  or  in  association  with  only  small 
amounts  of  any  one  of  the  others.  For  discussion  of  the  occur- 
rence of  the  iron  ores  see,  therefore,  under  hematite,  page  184; 
magnetite,  page  189;  limonite,  page  200;  and  siderite,  page  210. 

Hematite  is  by  far  the  most  important  ore  of  iron,  forming  in 
the  United  States  about  nine-tenths  of  the  ore  produced.  Limo- 
nite and  magnetite  form  each  about  one-twentieth  of  the  total, 
while  the  amount  of  siderite  produced  is  almost  negligible. 
Hematite  ore  comes  chiefly  from  the  various  Lake  Superior  dis- 


LEAD  319 

tricts  and  to  a  much  less  extent  from  Alabama.  Limonite  is 
found  in  the  Appalachian  states,  and  magnetite  in  New  York, 
New  Jersey  and  Pennsylvania.  Siderite  is  obtained  from  Ohio. 

Nearly  one-half  of  the  world's  production  of  iron  ore  comes 
from  the  United  States;  the  amount  produced  from  Minnesota 
alone  nearly  if  not  quite  equals  that  produced  in  any  other 
country.  Germany  and  Great  Britain,  Spain  and  France,  are 
notable  producers  of  iron. 

The  uses  of  iron  and  steel  are  too  well  known  to  need  dis- 
cussion. Copperas,  or  green  vitriol,  FeS04.7H20,  is  the  most 
important  salt  of  iron,  being  used  in  dyeing,  in  making  inks, 
Prussian  blue,  rouge,  and  as  a  disinfectant.  Rouge,  Fe203,  is 
used  as  a  polishing  powder  and  as  a  red  paint.  Considerable 
amounts  of  soft  iron  ore,  known  as  paint  ore,  are  ground  for 
mineral  paints,  such  as  ocher,  umber,  sienna,  etc. 

Lead. 

Galena,  PbS.  Vanadinite,  Pb4(PbCl)(V04)3. 

Cerussite,  PbC03.  Anglesite,  PbS04. 

Phosgenite,  (PbCl)C03.  Crocoite,  PrCr04. 

Pyromorphite,  Pb4(PbCl)(P04)3. 

Mimetite,  Pb4(PbCl)(As04)3.       Wulfenite,  PbMo04. 

Galena  is  the  usual  primary  ore  of  lead  and  furnishes  by  far 
the  greater  part  of  the  metal.  Cerussite  and  anglesite  are 
secondary  minerals  which  occur  in  smaller  amounts  in  the  oxi- 
dized zone  of  lead  deposits.  Galena  occurs  most  commonly 
associated  with  zinc  ores,  especially  sphalerite,  or  in  connection 
with  silver  ores.  Lead,  which  is  derived  from  ores  that  are  free 
from  silver,  is  known  as  "soft  lead,"  while  " desilverized"  lead, 
which  is  obtained  from  silver  ores,  is  known  as  "hard  lead." 
Lead  ores  are  most  commonly  found  as  replacement  deposits  in 
limestone  rocks,  either  in  the  form  of  beds  or  irregular  bodies, 
or  as  small  masses  disseminated  through  a  stratum  of  the  rock. 
For  the  associations  and  distribution  of  lead  ores  see  under 
galena,  page  139. 

Metallic  lead  is  used  in  the  form  of  sheet,  pipe,  etc.  It  is  used 
to  make  weights,  bullets  and  shot.  It  is  a  constituent  of  various 


320  MANUAL  OF  MINERALOGY 

alloys  such  as  solder  (lead  and  tin),  type  metal  (lead  and  anti- 
mony), low-fusing  alloys  (lead,  bismuth  and  tin).  A  large 
.amount  of  lead  is  used  in  the  form  of  the  basic  carbonate, 
(Pb.OH)2Pb(C03)2,  which  is  known  as  white  lead,  and  is  very 
valuable  as  a  paint.  The  oxides  of  lead,  litharge,  PbO,  and 
minium,  Pb304,  are  used  in  making  fine  grades  of  glass,  in  glaz- 
ing earthenware  and  as  pigments.  Lead  chromates  are  used  as 
yellow  and  red  paints.  Lead  acetate,  known  as  sugar  of  lead, 
has  important  uses  in  various  industries. 

Manganese. 

Alabandite,  MnS.  Psilomelane,  Mn02,  MnO,  etc. 

Franklinite,  (Fe,Mn,Zn)(Fe,Mn)204. 
Braunite,  Mn(Mn,Si)03.  Wad,  mixture  of  oxides. 

Manganite,  Mn2(OH)202.          Rhodochrosite,  MnC03. 
Pyrolusite,  Mn02.  Rhodonite,  MnSi03. 

Manganese  is  an  element  that  is  widely  distributed  in  small 
amounts.  Traces  of  it  at  least  are  to  be  found  in  most  rocks.  It 
most  commonly  occurs  in  silicates,  oxides  and  carbonates.  The 
oxides  are  the  most  abundant,  and  practically  all  of  the  metal 
is  derived  from  them. 

The  ore  deposits  of  manganese  are  ordinarily  of  secondary 
origin.  The  manganese  existing  in  the  rock-making  silicates, 
through  the  agency  of  weathering  processes,  is  changed  to  an 
oxide.  By  some  process  of  concentration  these  minerals  are 
often  gathered  together  into  irregular  bodies  lying  in  residual 
clays.  At  times  the  manganese  oxides  occur  associated  with 
iron  oxides,  and  when  this  is  the  case  the  two  are  smelted  to- 
gether to  form  directly  an  iron-manganese  alloy  used  in  making 
steel.  Manganese  minerals  also  frequently  occur  as  gangue 
minerals  in  connection  with  silver  ores.  A  manganese  ore  to 
be  of  commercial  value  should  contain  at  least  40  per  cent  of 
metallic  manganese  and  be  low  in  percentages  of  phosphorus 
and  silica. 

Manganese  is  obtained  in  the  United  States  from  the  following 
materials:  manganese  ores,  manganiferous  iron  ores,  manganif- 


MERCURY  321 

erous  silver  ores,  and  from  the  residuum  left  from  smelting  the 
zinc  ores  of  Franklin  Furnace,  New  Jersey.  Manganese  ores  are 
found  in  commercial  deposits  in  Virginia,  Georgia,  Arkansas  and 
California.  Manganif erous  iron  ores  are  found  in  Virginia,  and  at 
various  places  in  the  Lake  Superior  iron-ore  districts.  Manga- 
nif erous  silver  ores  are  found  in  the  Rocky  Mountain  and  Great 
Basin  regions,  the  principal  locality  being  Leadville,  Colorado. 
The  zinc  ores  of  Franklin  Furnace,  New  Jersey,  contain  small  per- 
centages of  manganese,  chiefly  in  the  mineral  franklinite,  and  in 
the  smelting  of  them  the  manganese  remains  in  the  residuum  from 
which  it  is  later  obtained.  This  is  the  most  important  source 
of  manganese  at  present  in  the  United  States.  Because  of  the 
small  domestic  production  of  manganese  ores  large  amounts 
have  to  be  imported.  These  come  largely  from  India  and  Brazil. 

Manganese  is  chiefly  used  in  the  form  of  alloys,  those  with 
iron  being  the  most  important.  Spiegeleisen  is  an  alloy  of  iron 
and  manganese  containing  below  20  per  cent  of  manganese, 
while  ferromanganese  contains  manganese  ranging  in  amount 
from  20  to  90  per  cent.  These  alloys  are  extensively  used  in 
the  manufacture  of  steel.  They  serve  to  take  away  any  oxygen 
that  might  be  in  the  iron,  the  oxygen  uniting  with  the  manganese 
and  going  into  the  slag.  They  serve  also  to  introduce  carbon 
into  the  steel  and  to  prevent  its  oxidation,  and  also  to  counteract 
the  bad  effects  of  sulphur  and  phosphorus.  Manganese  has 
also  of  itself  a  hardening  influence  on  steel.  For  these  reasons 
manganese  steels  have  a  wide  use. 

Chemical  uses  of  manganese  compounds  include  the  use  of 
the  oxide,  pyrolusite,  Mn02,  as  an  oxidizer  in  the  manufacture 
of  chlorine,  bromine  and  oxygen,  as  a  drier  in  paints  and  var- 
nishes, as  a  decolorizer  of  glass,  and  in  the  dry-cell  battery. 
Potassium  permanganate  is  used  as  a  disinfectant.  Manganese 
is  used  in  printing  calico  and  for  coloring  bricks,  pottery  and 
glass. 

Mercury. 

Cinnabar,  HgS. 

Mercury,  or  quicksilver,  is  neither  abundant  nor  widespread 
in  its  occurrence.  The  native  metal  is  sometimes  found  and 


322  MANUAL  OF  MINERALOGY 

other  rare  minerals  of  mercury  are  occasionally  noted,  but 
practically  the  only  ore  of  the  metal  is  the  sulphide,  cinnabar. 
For  the  occurrence  and  distribution  of  mercury,  therefore,  see 
under  cinnabar,  page  144. 

The  most  important  use  of  mercury  is  in  the  amalgamation 
process  for  recovering  gold  and  silver  from  their  ores.  It  is 
used  in  the  form  of  an  amalgam  with  tin  in  " silvering"  mirrors. 
It  is  used  in  thermometers,  barometers,  etc.  Mercury  salts, 
especially  calomel,  are  used  in  medicine.  The  sulphide  is  used 
as  the  pigment  called  vermilion. 

Molybdenum. 
Molybdenite,  MoS2.  Wulfenite,  PbMo04. 

Molybdenum  is  a  rare  element  occurring  chiefly  as  the  sul- 
phide, molybdenite.  More  rarely  wulfenite  may  serve  as  an 
ore.  See  under  molybdenite,  page  137,  and  under  wulfenite, 
page  308,  for  their  occurrence  and  distribution.  Only  a  small 
amount  of  molybdenum  is  produced  in  the  United  States. 

Molybdenum  is  used  to  a  small  extent  as  a  steel-hardening 
metal.  In  the  form  of  ammonium  molybdate  it  is  used  as  a 
chemical  reagent,  as  a  fireproofing  material,  and  as  a  disin- 
fectant. Molybdenum  compounds  are  also  used  to  color  leather 
and  rubber. 

Nickel. 

Pentlandite,  (Ni,Fe)S.  Chloanthite,  NiAs2. 

Millerite,  NiS.  Gersdorffite,  NiAsS. 

Niccolite,  NiAs.  Genthite,  Ni2Mg2Si3Oi0.6H20(?). 

Nickeliferous  Pyrrhotite.  Garnierite,  noumeaite,  H2NiSi04(?). 

LinnsBite,  (Co,Ni,Fe)3S4. 

Nickel  is  a  comparatively  rare  element,  found  often  associated 
with  cobalt.  Its  minerals  are  frequently  found  in  small  amounts 
in  connection  with  magnesian  igneous  rocks,  where  it  is  com- 
monly associated  with  chromite.  Only  a  few  localities  produce 
the  metal  in  commercial  quantities,  the  world's  output  coming 
mostly  from  the  nickeliferous  pyrrhotite  ores  of  Sudbury,  On- 


PLATINUM  323 

tario,  Canada,  or  from  the  silicate  (garnierite)  ores  of  New  Cale- 
donia. The  production  of  nickel  from  ores  mined  in  the  United 
States  is  very  small. 

The  chief  use  of  nickel  is  in  various  alloys.  Nickel  steel,  con- 
taining about  3.5  per  cent  of  nickel,  has  a  wide  use  because  of  its 
great  strength  and  toughness.  Other  alloys  are  German  silver 
(nickel,  zinc  and  copper) ;  metal  for  coinage  (nickel  and  copper) . 
Large  amounts  of  nickel  are  used  in  nickel  plating. 

Platinum. 

Native  Platinum,  Pt,  with  some  iron  and  traces  of  the  rare 
platinum  metals.  Sperrylite,  PtAs2. 

Platinum  is  a  rare  element  which  usually  occurs  native.  Its 
only  known  compound  occurring  as  a  mineral  is  the  arsenide, 
sperrylite,  which  has  been  found  very  sparingly  in  two  or  three 
localities  in  association  with  copper  and  nickel  ores.  Platinum 
is  characteristically  found  associated  with  the  magnesian  rocks 
called  peridotites  and  often  with  chromite.  The  only  commer- 
cial deposits  of  platinum  so  far  known  are  placer  deposits,  the 
materials  of  which  have  been  derived  from  the  weathering  of 
the  rocks  that  contained  the  platinum  in  disseminated  particles. 
For  the  occurrence  and  distribution  of  platinum  see  page  131. 

The  uses  of  platinum  chiefly  depend  upon  its  high  fusing  point 
(1700°  to  1800°  C.)  and  its  resistance  to  chemical  reagents.  It 
is  valuable  for  all  sorts  of  laboratory  apparatus,  such  as  crucibles, 
dishes,  spoons,  etc.  It  is  used  in  the  sulphuric  acid  industry 
for  concentrating  kettles  and  also  in  the  contact  process  for  the 
manufacture  of  the  acid  in  the  form  of  finely  divided  platinum, 
in  contact  with  which  the  acid  is  formed.  It  is  largely  used  as 
wire  to  form  the  electrical  connections  with  the  filaments  of 
incandescent  electric  lights.  It  is  used  in  jewelry,  particularly 
as  the  setting  for  diamonds,  in  dentistry  in  the  making  of  false 
teeth,  in  electrical  heating  apparatus,  for  sparking  plugs  in  ex- 
plosion motors,  in  the  measuring  of  high  temperatures,  in  elec- 
trical contacts,  etc.  Potassium  chloro-platinate,  2KCl.PtCl2,  is 
employed  in  photography. 


324  MANUAL  OF  MINERALOGY 

Silver. 

Native  Silver,  Ag.  Proustite,  3Ag2S.As2S3. 

Argentite,  As2S.  Stephanite,  5Ag2S.Sb2S3. 

Stromeyerite,  Ag2S.Cu2S.  Polybasite,  9Ag2S.Sb2S3. 

Sylvanite,  AgAuTe4.  Cerargyrite,  AgCl. 

Pyrargyrite,  3Ag2S.Sb2S3.  Embolite,  Ag(Cl,Br). 

It  is  to  be  noted  that  none  of  the  silver  minerals  contain  oxy- 
gen, the  most  important  series  being  included  in  the  sulphide 
and  sulpho-salt  "groups.  Besides  the  distinctively  silver  min- 
erals listed  above,  several  minerals  of  other  metals  contain  at 
times  sufficient  silver  to  make  them  valuable  ores  of  the  metal. 
Most  important  among  these  are  the  argentiferous  varieties  of 
galena,  chalcocite,  bornite,  chalcopyrite  and  tetrahedrite.  These 
minerals  form  the  most  common  ores  of  silver,  either  because  of 
the  small  amounts  of  silver  which  they  contain,  or  the  small 
amounts  of  silver  minerals  associated  with  them. 

The  important  ores  of  silver  can  be  divided  into  three  main 
classes,  namely,  the  siliceous  ores,  copper  ores  and  lead  ores. 
The  siliceous  ores  are  those  ores  which  contain  large  propor- 
tions of  quartz  with  small  amounts  of  gold  and  silver  minerals 
and  are  comparatively  free  from  other  metals.  Most  of  them 
contain  both  gold  and  silver,  the  gold  value  being  often  in  excess 
of  the  silver  value.  The  chief  districts  in  which  this  type  of 
silver  ore  is  produced  are  Tonopah  in  Nevada;  the  San  Juan, 
Leadville  and  Aspen  districts  in  Colorado;  Granite,  Jefferson 
and  Silverbow  counties  in  Montana;  and  in  various  districts 
in  Idaho,  Arizona,  California,  South  Dakota  and  Utah.  The 
important  deposits  of  copper  ores  which  contain  a  notable 
amount  of  silver  are  found  at  Butte  in  Montana;  at  the  Bingham 
and  Tintic  districts  in  Utah;  at  the  Bisbee,  United  Verde  and 
Silver  Bell  districts  in  Arizona;  in  Shasta  County,  California; 
and  at  various  places  in  Idaho,  Michigan  and  Colorado.  The 
important  deposits  of  lead  ore  that  produce  silver  are  to  be 
found  at  the  Cceur  d'Alene  district  in  Idaho;  at  the  Bingham 
and  Tintic  districts  in  Utah;  at  the  Creede,  San  Juan  and  Lead- 
ville districts  in  Colorado;  and  at  various  districts  in  Nevada, 


TIN  325 

Montana  and  Arizona.  For  the  production  of  these  different 
classes  of  silver  ores  see  Appendix  II. 

The  important  foreign  countries  for  the  production  of  silver 
are  Mexico,  Canada  and  Australia.  In  Mexico  the  chief  dis- 
tricts are  Guanajuato,  Pachuca,  El  Oro,  Parral  and  Santa  Eulalia; 
in  Canada  in  the  Boundary  and  Kootenai  districts  in  British 
Columbia  and  the  Cobalt  district  in  Ontario;  in  Australia 
chiefly  from  the  Broken  Hill  district  in  New  South  Wales. 

In  connection  with  silver  ores  the  following  facts  are  of  in- 
terest. Owing  to  the  high  value  of  silver,  only  a  small  per- 
centage of  the  metal  in  an  ore  is  sufficient  to  make  it  valuable. 
For  instance,  an  ore  that  contained  only  0.34  per  cent  of  silver 
would  yield  100  ounces  to  the  ton,  which  is  an  amount  much 
larger  than  usual.  In  giving  the  assay  value  of  an  ore,  the 
amount  of  silver  is  usually  stated  in  ounces  per  ton  of  ore. 
Lead-silver  ores  are  of  value  because  in  the  smelting  the  silver 
will  be  taken  up  by  the  lead.  Ores  containing  calcium  car- 
bonate and  iron  and  manganese  minerals  are  of  value  because 
of  the  service  of  these  materials  in  fluxing  the  ore.  Zinc  min- 
erals detract  from  the  value  of  an  ore  because  of  the  added 
difficulty  in  smelting  caused  by  their  presence. 

The  uses  of  silver  for  coinage,  for  various  useful  and  ornamental 
objects  and  for  plating  are  too  well  known  to  need  discussion. 
The  standard  silver  coin  for  the  United  States  contains  nine 
parts  of  silver  to  one  of  copper.  Silver  salts  are  used  in  photog- 
raphy and  caustic  silver  (AgN03)  is  employed  in  medicine. 

Tin. 

Stannite,  Cu2S.FeS.SnS.  Cassiterite,  Sn02. 

The  only  ore  of  tin  of  importance  is  the  oxide,  cassiterite. 
This  is  a  mineral  which,  while  occurring  in  small  quantities  in 
many  localities,  is  found  only  in  a  comparatively  few  commercial 
deposits.  For  the  occurrence  and  distribution  of  the  mineral 
see  page  193.  The  United  States  at  present  produces  only  a 
small  amount  of  tin  ore. 

Tin  is  chiefly  used  in  the  coating  or  "tinning"  of  metals,  es- 
pecially iron.  The  tin  plate  thus  formed  is  used  in  roofing,  in 


326  MANUAL  OF  MINERALOGY 

various  utensils,  etc.  An  amalgam  of  tin  and  mercury  is  used 
in  "silvering"  mirrors.  Various  alloys  are  valuable,  such  as 
solder  (tin  and  lead),  bronze  and  bell  metal  (copper  and  tin). 
The  artificial  oxide  of  tin  is  used  as  a  polishing  powder.  Stannic 
chloride  is  employed  as  a  mordant  in  dyeing. 

Titanium. 

Ilmenite,  titanic  iron,  FeTi03       Octahedrite,  Ti02. 

with  MgTi03  and  Fe203.  Brookite,  Ti02. 

Rutile,  Ti02.  Titanite,  CaTiSi05. 

Titanium  is  a  rare  element,  but  is  quite  widely  distributed  in 
small  quantities.  In  the  form  of  the  minerals  rutile  and  titanite 
it  is  present  in  most  igneous  rocks.  Ilmenite  is  commonly 
found  in  the  basic  igneous  rocks,  and  is  often  associated  with 
magnetic  iron  ores. 

Very  little  titanium  ore  is  produced  in  the  United  States. 
Rutile  deposits  occur  in  Virginia,  and  some  of  the  Adirondack 
magnetite  deposits  contain  considerable  ilmenite. 

The  present  uses  of  titanium  are  rather  limited.  It  has  been 
used  in  steel  and  cast  iron,  in  which  it  serves  to  eliminate  the 
oxygen  and  nitrogen.  It  is  also  said  to  give  a  high  tensile 
strength  and  great  ductility  to  the  steel.  It  is  being  used  to 
some  extent  in  the  manufacture  of  electrodes  for  arc  lights. 
The  oxide  is  used  to  give  a  yellow  color  to  porcelain,  and  to  give 
a  natural  color  to  false  teeth. 

Tungsten. 

Wolframite,  (Fe,Mn)W04.         Scheelite,  CaW04. 
Hiibnerite,  MnW04. 

Tungsten  is  a  rare  acid-forming  heavy  metal  found  chiefly  in 
the  tungstates  of  iron  and  calcium,  wolframite  and  scheelite. 
For  the  occurrence  and  distribution  of  these  minerals  see  under 
wolframite,  page  307,  and  scheelite,  page  308. 

The  most  important  use  to  which  tungsten  is  put  is  as  a  steel- 
hardening  metal.  Tungsten  steels  hold  their  temper  at  high 
temperatures  and  are  therefore  valuable  for  the  making  of  high- 


ZINC  327 

speed  tools,  etc.  Because  of  its  high  fusing  point  metallic 
tungsten  is  used  as  a  filament  in  incandescent  electric  lights. 
Sodium  tungstate  is  used  in  fireproofing  cloth  and  as  a  mordant 
in  dyeing.  Calcium  tungstate  is  used  as  the  luminous  screen  in 
X-ray  apparatus. 

Vanadium. 

Roscoelite,  H8K2(Mg,Fe)(Al,V)4(Si03)2(?). 
Vanadinite,Pb4(PbCl)(V04)3.Carnotite,K(U02)2(V04)2.3H20(?). 

Vanadium  is  an  acid-forming  metal  which  is  known  in  a  num- 
ber of  very  rare  minerals.  The  three  listed  above  are  the  only 
ones  which  occur  in  sufficient  quantities  in  the  United  States  to 
be  available  for  ores.  Roscoelite  is  a  green  micaceous  mineral 
containing  about  2  per  cent  of  metallic  vanadium.  It  is  found 
in  a  soft  sandstone  near  Placerville,  Col.  Carnotite  is  a  sulphur- 
yellow  pulverulent  mineral  of  doubtful  composition  which  is 
found  in  sandstones  in  several  districts  in  Colorado  and  Utah, 
near  the  boundary  line  between  the  two  states.  Vanadinite  is 
a  secondary  lead  mineral  which  is  found  sparingly  in  the  oxi- 
dized zones  of  certain  lead  deposits  in  Arizona  and  New  Mexico. 
All  of  these  ores  are  low  grade,  and  are  worked  only  in  a  small 
way  and  at  intervals.  The  chief  supply  of  vanadium  ores  at 
present  comes  from  Peru,  where  there  are  large  deposits  of  an 
impure  carbonaceous  sulphide  of  vanadium,  known  as  patronite. 

Vanadium  is  used  chiefly  in  steel,  and  is  said  to  give  it  great 
tensile  and  elastic  strength.  Metavanadic  acid,  HV03,  is  used 
as  a  yellow  pigment,  known  as  vanadium  bronze.  Vanadium 
oxide  serves  as  a  mordant  in  dyeing. 

Zinc. 

Sphalerite,  ZnS.  Smithsonite,  ZnC03. 

Zincite,  ZnO.  Willemite,  Zn2Si04. 

Franklinite,  (Fe,Zn,Mn)  (Fe,Mn)203. 

Calamine,  (ZnOH)2SiO». 

The  sulphide,  sphalerite,  is  the  one  common  primary  ore  of 
zinc.  The  carbonate,  smithsonite,  and  the  silicate,  calamine, 
are  usually  associated  with  sphalerite  deposits  as  secondary 


328  MANUAL  OF  MINERALOGY 

minerals.  The  three  minerals,  zincite,  franklinite  and  willemite, 
are  found  in  unique  deposits  at  Franklin  Furnace,  New  Jersey. 
Together  with  a  large  number  of  rare  and  unusual  minerals  they 
form  anticlinal  beds  lying  intercalated  in  a  limestone  series.  In 
general  sphalerite,  the  chief  ore  of  zinc,  is  found  in  irregular 
replacement  deposits  in  limestone.  It  is  very  frequently  inti- 
mately associated  with  lead  minerals.  For  its  occurrence  and 
distribution  see  page  142. 

Metallic  zinc,  or  spelter,  as  it  is  called,  is  chiefly  used  for  gal- 
vanizing iron,  as  an  alloy  with  copper  in  brass,  and  in  storage 
and  telegraph  batteries.  Zinc  dust  or  zinc  shavings  are  used  to 
precipitate  gold  from  its  solution  in  the  cyanide  process.  Large 
amounts  of  zinc  oxide,  or  zinc  white,  are  used  as  a  white  paint 
which  is  even  more  permanent  than  lead  paints.  Zinc  chloride 
is  used  as  a  wood  preservative. 


OCCURRENCE  AND  ASSOCIATION  OF  MINERALS. 

Although  minerals  are  found  in  many  modes  of  occurrence, 
and  in  an  almost  endless  variety  of  associations,  there  are,  how- 
ever, certain  frequent  and  important  ways  in  which  they  occur 
that  should  be  pointed  out.  An  understanding  of  the  condi- 
tions under  which  a  particular  mineral  is  usually  formed,  together 
with  a  knowledge  of  what  other  minerals  are  characteristically 
associated  with  it,  is  of  the  greatest  value.  On  the  following 
pages  is  given,  therefore,  a  brief  discussion  of  the  more  important 
modes  of  mineral  occurrence,  and  of  the  more  common  associa- 
tions observed. 

Rocks  and  Rock-making  Minerals. 

Since  by  far  the  greater  part  of  minerals  occur  as  rock  con- 
stituents a  short  description  of  the  more  important  rock  types 
and  of  the  common  rock-making  minerals  will  be  given  first. 
Only  the  barest  outline  of  the  subject  can  be  given  here  and  for 
more  detailed  information  the  reader  is  referred  to  one  of  the 
textbooks  which  treat  more  particularly  of  petrology. 


IGNEOUS  ROCKS  329 

Rocks  may  be  divided  into  three  main  divisions,  namely: 
I.   Igneous. 
II.   Sedimentary. 
III.   Metamorphic. 

I.   Igneous  Rocks. 

Igneous  Rocks,  as  the  name  indicates,  are  those  which  have 
been  formed  by  the  cooling  and  consequent  solidification  of  a 
once  hot  and  fluid  mass  of  rock  material.  This  liquid  mass 
is  known  as  a  rock  magma.  A  magma,  in  a  measure,  is  like 
a  solution  containing  in  a  dissociated  condition  the  elements 
which,  when  the  mass  cools  sufficiently,  unite  to  form  the  various 
minerals  that  go  to  make  up  the  resulting  rock.  The  elements 
which  form  the  chief  constituents  of  the  magmas  of  igneous 
rocks  are  oxygen,  silicon,  aluminium,  iron,  calcium,  magnesium, 
sodium  and  potassium,  named  in  the  order  of  their  abundance. 
When  a  magma  cools  these  elements  unite  to  form  various 
mineral  molecules,  which,  when  the  point  of  supersaturation 
is  reached,  crystallize  out  to  form  the  minerals  of  the  rock. 
Certain  compounds  under  similar  conditions  crystallize  out 
of  the  fluid  mass  earlier  than  do  others.  In  most  igneous 
rocks  a  more  or  less  definite  order  of  crystallization  for  their 
mineral  constituents  can  be  determined.  In  general  the  more 
basic  minerals  or  those  which  contain  the  smaller  amounts  of 
silica,  which  is  the  acid  element  in  igneous  rocks,  are  observed 
to  crystallize  first  and  the  more  acid  minerals  last.  Among  the 
commoner  rock-making  minerals  the  following  would  be  the 
usual  order  of  crystallization;  iron  oxides  like  magnetite  first, 
then  the  ferro-magnesian  minerals  like  pyroxene,  next  the 
plagioclase  feldspars,  then  orthoclase  and  lastly  quartz. 

The  type  of  minerals  to  be  found  in  any  igneous  rock  would 
depend  chiefly  upon  the  chemical  composition  of  the  original 
magma.  If  the  magma  was  acid  in  character,  i.e.,  had  a  high 
percentage  of  silica,  the  resulting  rock  would  contain  the  more 
acid  minerals  and  an  abundance  of  free  quartz.  It  would 
usually  be  light  in  color.  If,  on  the  other  hand,  the  magma  had 


330  MANUAL  OF  MINERALOGY 

a  low  percentage  of  silica,  or  in  other  words  was  basic  in  char- 
acter, the  resulting  rock  would  contain  the  more  basic  minerals 
and  would  not  show  free  quartz.  It  would  also  in  general  be 
dark  in  color. 

In  addition  to  the  wide  variation  in. chemical  and  mineral 
composition  shown  by  igneous  rocks  there  is  also  a  variation  in 
their  physical  structure.  This  is  dependent  upon  the  mode  of 
origin  of  the  rock.  If  a  rock  has  been  formed  from  a  magma 
buried  at  a  considerable  depth  in  the  crust  of  the  earth  it  must 
have  cooled  very  slowly  and  taken  a  long  period  of  time  for  its 
gradual  crystallization  and  solidification.  Under  these  condi- 
tions the  mineral  particles  have  had  the  opportunity,  because 
of  the  slowness  of  crystallization,  to  grow  to  considerable  size. 
A  rock  having  such  a  deep-seated  origin  has,  therefore,  a  coarse- 
grained structure  and  the  various  minerals  that  go  to  form  the 
rock  can  in  general  be  differentiated  and  recognized  by  the 
unaided  eye.  Such  rocks  are  commonly  termed  plutonic. 

On  the  other  hand,  if,  by  volcanic  forces,  the  magma,  has  been 
extruded  upon  the  surface  of  the  earth  or  intruded  in  the  form 
of  dikes  into  the  rocks  lying  close  to  the  surface,  its  subsequent 
cooling  and  solidification  go  on  quite  rapidly.  Under  these  con- 
ditions the  mineral  particles  have  little  chance  to  grow  to  any 
size  and  the  resulting  rock  is  fine-grained  in  character.  In  some 
cases,  indeed,  the  cooling  has  been  too  rapid  to  allow  the  separa- 
tion of  any  minerals  and  the  resulting  rock  is  like  a  glass.  Ordi- 
narily the  mineral  constituents  of  such  a  rock  are  only  to  be 
definitely  recognized  by  a  microscopic  examination  of  a  thin 
section  of  the  rock.  Such  igneous  rocks  are  known  as  volcanic 
rocks. 

An  igneous  rock,  because  of  the  mode  of  its  formation,  con- 
sists of  crystalline  particles  which  may  be  said  to  interlock  with 
each  other.  In  other  words,  it  is  a  solid  mass,  and  each  mineral 
particle  is  intimately  and  firmly  embedded  in  the  surrounding 
particles.  This  structure  will  enable  one  ordinarily  to  distin- 
guish an  igneous  from  a  sedimentary  rock,  the  latter  being  com- 
posed of  grains  which  do  not  interlock  with  each  other  but  stand 
out,  more  or  less,  by  themselves.  A  sedimentary  rock  is  not 


PLUTONIC,   COARSE-GRAINED  ROCKS  331 

so  firm  and  coherent  as  an  igneous  rock.  Further  the  texture 
of  an  igneous  rock  is  the  same  in  all  directions  and  it  forms  a 
fairly  uniform  and  homogeneous  mass.  This  characteristic  will 
enable  one  to  distinguish  an  igneous  from  a  metamorphic  rock, 
since  the  latter  shows  a  more  or  less  definite  parallel  arrange- 
ment of  its  minerals  and  a  banded  structure. 

Because  of  the  almost  infinite  variation  possible  in  the  chemi- 
cal composition  of  their  magmas,  and  because  of  the  various 
conditions  under  which  they  may  form,  igneous  rocks  show  like- 
wise a  wide  variation  in  character.  The  more  common  and 
important  types,  however,  are  very  briefly  described  below. 

Plutonic,  Coarse-grained  Rocks. 

1.  Granite.     A  granite  is  a  medium-  to  coarse-grained,  light- 
colored  rock  having  an  even  texture  and  consisting  chiefly  of 
quartz   and   a   feldspar.     Frequently   both   orthoclase   and   a 
plagioclase  feldspar,'  and  usually  also  small  amounts  of  mica  or 
hornblende  are  present.     The  feldspars  can  be  recognized  by 
their  color  and  cleavage.     Frequently  the  orthoclase  is  colored 
flesh-color  or  red,  while  the  soda-lime  feldspar  is  usually  white. 
The  quartz  is  recognized  by  its  glassy  luster  and  conchoidal 
fracture.     It  is  usually  white  or  smoky-gray  in  color  and  is 
found  in  irregular  grains  filling  up  the  interstices  between  the 
other  minerals.    The  mica,  which  may  be  either  muscovite  or 
biotite,  is  to  be  recognized  by  its  cleavage.     Granite  is  a  common 
rock  type. 

2.  Syenite.     A  syenite  is  a  medium-  to  coarse-grained  light- 
colored  rock  with  an  even  texture  and  much  like  a  granite  in 
appearance.     It  is  to  be  distinguished  from  granite,  however,  by 
the  fact  that  it  contains  little  or  no  quartz.     Its  chief  minerals 
are  the  feldspars,  with  more  or  less  hornblende,  mica  or  pyroxene. 
A  variety,  known  as  nephelite-syenite,  is  characterized  by  the 
presence  of  considerable  amounts  of  nephelite.    Another  variety, 
called  anorthosite,   is   composed  chiefly  of  labradorite.    The 
feldspars,  mica  and  hornblende  may  be  distinguished  as  de- 
scribed under  granite.    The  pyroxene  resembles  hornblende  in 
appearance,  but  does  not  show  as  good  a  prismatic  cleavage. 


332  MANUAL  OF  MINERALOGY 

Nephelite  is  recognized  by  its  lack  of  a  distinct  cleavage  and  its 
oily  and  greasy  luster.     Syenites  are  not  very  common. 

3.  Diorite.     Diorite  is  a  medium-  to  coarse-grained  dark  gray 
or  greenish  colored  rock  having  an  even  texture  and  consisting 
chiefly  of  hornblende  and  a  feldspar,  in  which  the  hornblende 
predominates.     Often  fine  grains  of  iron  ore  may  be  observed, 
and  frequently  considerable  amounts  of  biotite.     It  is  a  common 
rock  type. 

4.  Gabbro.     Gabbro  is  a  medium-  to  coarse-grained  dark  gray 
to  greenish  black  rock  with  an  even  texture  composed  chiefly 
of.  pyroxene  and  a  feldspar.     It  is  closely  similar  to  diorite,  the 
distinction  lying  in  the  fact  that  it  contains  pyroxene  instead 
of  amphibole.    These  two  minerals,  as  they  occur  in  these  rocks, 
cannot  always  be  told  apart  by  a  megascopic  examination. 
The  pyroxene  is  usually  in  small  crystal  grains  with  rather  poor 
prismatic  cleavages  which  are  at  nearly  right  angles  to  each 
other.     Hornblende  is  more  liable  to  be  in  longer  prismatic 
crystals  and  shows  better  cleavages,  the  angle  of  which  is  about 
125°.     It  is  a  common  rock. 

5.  Dolerite.     This  is  a  name  given  to  those  varieties  of  diorite 
and  gabbro  which  are  too  fine-grained  in  character  to  enable 
one  to  tell  megascopically  whether  the  dark-colored  mineral 
which  they  contain  is  hornblende  or  pyroxene. 

6.  Peridotite.     A  peridotite  is  a  medium-  to  coarse-grained 
dark  green  to  black  rock  with  an  even  texture  which  consists 
wholly  of  ferromagnesian  minerals.     These  are  chiefly  olivine, 
pyroxene  and  hornblende.     As  one  or  the  other  of  these  minerals 
predominates,  various  variety  names  are  used,  such  as  dunite  for 
an  olivine  rock  and  pyroxenite  and  hornblendite  for  respectively 
pyroxene  and  hornblende  rocks.     Common  accessory  minerals 
found  in  these  rocks  are  ilmenite,  chromite  and  garnet.    The 
peridotites  are  not  very  common  in  their  occurrence. 

Volcanic,  Fine-grained  Igneous  Rocks. 

Because  of  their  very  fine-grained  structure  volcanic  rocks 
cannot  in  general  be  readily  told  apart.  A  number  of  different 
types  are  recognized,  the  distinction  between  them  being  based, 


VOLCANIC,  FINE-GRAINED  IGNEOUS  ROCKS    333 

however,  chiefly  upon  microscopic  study.  In  the  field  only  an 
approximate  classification,  depending  upon  whether  the  rock 
is  light  or  dark  in  color,  can  be  made.  A  brief  description  of 
these  two  types  of  volcanic  rocks  follows. 

1.  Felsite.     This  is  a  dense  fine-grained  rock  type  with  a  stony 
texture  an,d  includes  all  colors  except  dark  gray,  dark  green  or 
black.     These  rocks  may,  by  the  aid  of  a  lens,  still  show  a  very 
fine-grained  structure  or  their  mineral  constituents  may  occur 
in  such  small  particles  as  to  give  them  a  dense  and  homogeneous, 
often  a  flinty,  appearance.     By  microscopic  study  the  felsites 
have  been  divided  into  the  following  groups;  rhyolite,  consisting 
chiefly  of  alkaline  feldspars  and  quartz;   dacite,  lime-soda  feld- 
spars and  quartz;    trachyte,  alkaline  feldspars  with  little  or  no 
quartz;    andesite,  soda-lime  feldspars  with  little  or  no  quartz; 
phonolite,  alkaline  feldspars  and  nephelite.     As  a  rule  these 
varieties  are  not  to  be  distinguished  from  each  other  in  the  field. 
The  felsites  are  widespread  in  their  occurrence,  being  found  as 
dikes  and  sheets  intruded  into  the  upper  part  of  the  earth's  crust 
or  as  lava  flows  which  have  been  poured  out  upon  the  earth's 
surface. 

2.  Basalt.     The  basalts  are  dense  fine-grained  rocks  that  are 
of  very  dark  color,  green  or  black.    They  are  composed  of  micro- 
scopic grains  of  a  soda-lime  feldspar  with  pyroxene,  iron  ore, 
often  more  or  less  olivine  and  at  times  biotite  or  hornblende. 
These  rocks  are  formed  under  the  same  conditions  as  the  felsites 
and  are  to  be  found  occurring  in  the  same  ways. 

3.  Glassy  Rocks.     Some  of  the  volcanic  rocks  have  cooled 
so  rapidly  that  they  are  wholly  or  in  part  made  up  of  a  glassy 
material  in  which  the  different  elements  have  not  had  the  neces- 
sary opportunity  to  group  themselves  into  definite  minerals. 
If  the  entire  rock  is  composed  of  glass  it  is  called  obsidian,  when 
it  has  a  bright  and  vitreous  luster;  pitchstone  when  its  luster  is 
dull  and  pitchy;  perlite  if  it  is  made  up  of  small  spheroids;  and 
pumice  if  it  has  a  distinctly  cellular  structure.    These  rocks 
may  also  have  distinct  crystals  of  various  minerals  embedded 
in  the  glass,  in  which  case  they  are  known  as  glass  porphyries  (see 
below  for  a  definition  of  a  porphyry)  or  vitrophyres. 


334  MANUAL  OF  MINERALOGY 

Porphyries.  Igneous  rocks  at  times  show  distinct  crystals  of 
certain  minerals  which  lie  embedded  in  a  much  finer-grained 
material.  These  larger  crystals  are  known  as  phenocrysts,  and 
the  finer-grained  material  as  the  groundmass  of  the  rock.  Rocks 
exhibiting  such  a  structure  are  known  as  porphyries.  The 
phenocrysts  may  vary  in  size  from  crystals  an  inch  or  more 
across  down  to  quite  small  individuals.  The  groundmass  may 
also  be  composed  of  fairly  coarse-grained  material  or  its  grains 
may  be  microscopic  in  size.  It  is  the  distinct  difference  in  size 
existing  between  the  phenocrysts  and  the  particles  of  the  ground- 
mass  that  is  the  distinguishing  feature  of  a  porphyry.  This 
peculiar  structure  is  due  to  certain  conditions  prevailing  during 
the  formation  of  the  rock  which  permitted  some  crystals  to  grow 
to  considerable  size  before  the  main  mass  of  the  rock  consolidated 
into  a  finer-  and  uniform-grained  material.  The  explanation  of 
the  reasons  why  a  certain  rock  should  assume  a  porphyritic 
structure  would  involve  a  more  detailed  discussion  than  it  is 
expedient  to  give  in  this  place.  Any  one  of  the  above  described 
types  of  igneous  rocks  may  have  a  porphyritic  variety,  such  as 
granite-porphyry,  diorite-porphyry,  felsite-porphyry,  etc.  Por- 
phyritic varieties  are  more  liable  to  occur  in  connection  with 
volcanic  rocks,  and  they  are  also  found  most  frequently  in  the 
case  of  the  more  acid  types. 

II.  Sedimentary  Rocks. 

Sedimentary  rocks  are  secondary  in  their  origin,  the  materials 
of  which  they  are  composed  having  been  derived  from  the  decay 
and  disintegration  of  some  previously  existing  rock  mass.  They 
have  been  formed  by  a  deposition  of  sediments  in  a  body  of 
water.  They  may  be  divided  into  two  classes,  depending  upon 
whether  their  origin  has  been  mechanical  or  chemical  in  its 
nature.  In  the  case  of  the  sedimentary  rocks  of  a  mechanical 
origin,  their  constituent  particles  have  been  derived  from  the 
disintegration  of  some  rock  mass,  and  have  been  transported 
by  streams  into  a  large  body  of  quiet  water,  where  they  have 
been  deposited  in  practically  horizontal  layers.  Sedimentary 


SEDIMENTARY  ROCKS  335 

rocks  of  chemical  origin  have  had  the  materials  of  which  they 
are  composed  dissolved  by  waters  circulating  through  the  rocks 
and  brought  ultimately  by  these  waters  into  a  sea,  where  through- 
some  chemical  change  they  are  precipitated  upon  its  floor,  also 
in  horizontal  layers.  These  horizontal  beds  of  sediments  are 
ultimately  consolidated  into  the  masses  known  as  sedimentary 
rocks. 

Sedimentary  rocks  are  therefore  characterized  by  a  parallel 
arrangement  of  their  constituent  particles  into  layers  and  beds 
which  are  to  be  distinguished  from  each  other  by  differences  in 
thickness,  size  of  grain  and  often  in  color.  It  is  to  be  noted, 
further,  that  sedimentary  rocks  in  general  are  composed  of  an 
aggregate  of  individual  mineral  particles,  each  of  which  stands 
out  in  a  way  by  itself  and  does  not  have  that  intimate  inter- 
locking relation  with  the  surrounding  particles  which  is  to  be 
seen  in  the  minerals  of  an  igneous  rock.  In  all  the  coarser- 
grained  sedimentary  rocks  there  is  some  material  which,  acting 
as  a  cement,  surrounds  the  individual  mineral  particles  and  binds 
them  together.  This  cement  is  usually  either  silica,  calcium 
carbonate  or  iron  oxide.  The  chief  minerals  to  be  found  in 
sedimentary  rocks  are  quartz  and  a  carbonate,  calcite  or  dolo- 
mite. These  give  rise  to  the  two  chief  types  of  sedimentary 
rocks,  the  sandstones  and  the  limestones.  A  brief  description 
of  these  rocks  follows. 

1.  Sandstone.  Sandstones  are  mechanical  in  their  origin, 
being  formed  by  the  consolidation  into  rock  masses  of  beds  of 
sand  and  gravel.  Usually  the  constituent  grains  are  rounded 
and  water-worn,  but  at  times  they  may  be  more  or  less  angular 
in  shape.  With  the  variation  in  the  size  of  the  mineral  particles 
the  rocks  themselves  vary  in  their  grain.  Coarse-grained  sand- 
stones formed  from  gravels  are  known  as  conglomerates.  The 
cement  which  serves  to  bind  the  sand  grains  together  may  be 
deposited  silica,  a  carbonate,  usually  calcite,  an  iron  oxide, 
hematite  or  limonite,  or  fine-grained  argillaceous  or  claylike 
material.  The  color  of  the  rock  will  depend  in  large  measure 
upon  the  character  of  the  cement.  The  rocks  which  have  silica 
or  calcite  as  their  binding  material  are  light  in  color,  usually  pale 


336  MANUAL  OF  MINERALOGY 

yellow,  buff,  white  to  gray,  while  those  that  contain  an  iron 
oxide  are  red  to  reddish  brown.  It  is  to  be  noted  that  when  a 
sandstone  breaks  it  is  usually  the  cement  that  is  fractured,  while 
the  individual  grains  remain  unbroken,  so  that  the  fresh  surfaces 
of  the  rock  have  a  granular  appearance  and  feeling.  The  chief 
mineral  of  sandstones  is  quartz,  but  at  times  a  rock  may  contain 
notable  amounts  of  feldspar  and  is  then  termed  an  arkose. 
Graywacke  is  a  sandstone,  usually  of  a  gray  color,  which  in  addi- 
tion to  quartz  and  feldspar  contains  particles  of  other  rocks  and 
minerals. 

2.  Shale.     The  shales  are  very  fine-grained  sedimentary  rocks 
which  have  been  formed  by  the  consolidation  of  beds  of  mud, 
clay  or  silt.    They  have  usually  a  thinly  laminated  structure. 
Their  color  is  commonly  some  tone  of  gray,  although  they  may 
be  white,  yellow,  brown,  green  to  black.     They  are  composed 
chiefly  of  kaolin,  mica,  etc.,  but  are  too  fine-grained  to  permit 
the  recognition  of  their  mineral  constituents  by  the  eye  alone. 
By  the  introduction  of  quartz  and  an  increase  in  the  size  of 
grain  they  grade  into  the  sandstones. 

3.  Limestone.     The  limestones  are  carbonate  rocks  composed 
usually  chiefly  of  calcite,  although  dolomite  may  also  be  at  times 
an  important  constituent.    The  carbonate  has  in  the  great 
majority  of  cases  been  extracted  from  the  sea  water  by  the 
agency  of  minute  organisms  and  then  deposited  in  beds  which 
ultimately  are  consolidated  into  rock.    These  rocks  are  usu- 
ally fine-  and  even-grained  in  structure  and  sometimes  quite 
dense.     Some  limestones  are  quite  pure  calcite,  while  others  con- 
tain clay  like  materials  and  various  oxides  as  impurities.    The 
color  of  a  limestone  is  usually  gray,  although  it  may  be  white, 
yellow,  brown  to  almost  black.     It  is  a  soft  rock,  to  be  easily 
scratched  by  a  knife.     It  will  effervesce  readily  in  any  common 
acid.     In  the  case  of  limestones  composed  of  dolomite,  however, 
the  acid  needs  to  be  heated.     Oolite,  or  oolitic  limestone,  is  a  vari- 
ety which  consists  of  an  aggregate  of  small  spherical  concretions. 
Chalk  is  a  very  fine-grained  friable  limestone  composed  of  shells 
of  minute  sea  animals  known  as  foraminifera.     Travertine  is  a 
deposit  of  calcium  carbonate  formed  by  springs.    A  fine  example 


METAMORPHIC  ROCKS  337 

exists  in  the  deposits  formed  by  the  Mammoth  Hot  Springs, 
Yellowstone  Park.  Marl  is  a  loose,  earthly  material  composed 
of  a  carbonate  mixed  with  clay  in  variable  amount. 

III.   Metamorphic  Rocks. 

Metamorphic  rocks  are  rocks  which  have  undergone  some 
chemical  or  physical  change  subsequent  to  their  original  forma- 
tion. This  change  has  been  brought  about  by  means  of  high  tem- 
perature and  pressure  aided  by  the  action  of  water  and  other 
chemical  agents.  The  changes  involve  the  formation  of  new 
minerals,  the  adding  or  subtracting  of  chemical  constituents  and 
a  physical  readjustment  of  the  mineral  particles  to  conform  to 
the  existing  pressure.  The  original  rock  from  which  a  metamor- 
phic  rock  has  been  derived  may  be  either  igneous  or  sedimentary. 
As  these  rocks  become  involved  in  movements  of  the  earth's  crust, 
they  are  subjected  to  extreme  pressures  accompanied  usually 
by  high  temperatures.  The  result  will  be  frequently  to  trans- 
form the  existing  minerals  into  others  more  stable  under  the 
new  conditions.  The  physical  structure  of  the  rock  will  also 
ordinarily  be  changed  during  the  process.  Because  of  the  pres- 
sure to  which  the  rock  is  subjected  the  mineral  particles  will  be 
more  or  less  broken  and  flattened  and  rearranged  in  parallel 
layers.  This  banded  or  laminated  character  given  by  the 
parallel  arrangement  of  its  minerals  is  the  most  striking  pecu- 
liarity of  a  metamorphic  rock.  Because  of  this  structure  a 
metamorphic  rock  can  be  distinguished  from  an  igneous  rock. 
Further,  in  the  great  majority  of  cases  a  metamorphic  rock  has 
a  crystalline  structure  which  distinguishes  it  from  a  sedimentary 
rock.  There  are,  of  course,  all  gradations  from  a  typical  meta- 
morphic rock  into  an  unaltered  sedimentary  rock  on  the  one 
hand  and  into  an  unaltered  igneous  rock  on  the  other.  The 
most  common  types  of  metamorphic  rocks  are  briefly  described 
below. 

1.  Gneiss.  When  the  word  gneiss  is  used  alone  it  usually 
refers  to  a  metamorphic  rock  composed  essentially  of  quartz, 
feldspar  and  a  mica.  The  quartz  and  feldspar  occur  together 
in  layers  which  are  separated  from  each  other  by  thin  drawn-out 


338  MANUAL  OF  MINERALOGY 

bands  of  'mica.  A  gneiss  has  usually  a  light  color,  although 
this  is  not  necessarily  so.  Various  varieties  of  gneiss  have  re- 
ceived distinctive  names,  most  of  which  are  self-explanatory,  like 
banded-gneiss,  lenticular-gneiss,  biotite-gneiss,  hornblende-gneiss, 
granite-gneiss,  diorite-gneiss,  etc.  Gneiss  is  a  very  common  rock 
type,  especially  in  regions  in  which  the  oldest  rocks,  those  of 
the  Archaean  age,  are  found.  Gneisses  have  been  more  com- 
monly derived  by  the  metamorphism  of  igneous  rocks,  mostly 
granites,  but  may  have  been  formed  from  sedimentary  rocks  as 
well. 

2.  Mica-schist.     Mica-schist  is  a  rock  composed  essentially 
of  quartz  and  a  mica,  usually  either  muscovite  or  biotite.    The 
mica  is  the  prominent  mineral,  occurring  in  irregular  leaves  and 
in  foliated  masses.     The  mica  plates  all  lie  with  their  cleavage 
planes  parallel  to  each  other  and  give  to  the  rock  a  striking  lam- 
inated or  " schistose"  structure.     The  mica-schists  frequently 
carry  characteristic  accessory  minerals,  such  as  garnet,  stauro- 
lite,  cyanite,  epidote,  hornblende,  etc.    They  may  have  been 
derived  from  either  an  igneous  or  a  sedimentary  rock.     Next  to 
the  gneisses,  they  are  the  most  common  metamorphic  rocks. 

3.  Quartzite.     As  its  name  indicates,  a  quartzite  is  a  rock 
composed   essentially  of  quartz.     It  is  a  firm,  compact  rock 
which  breaks  with  an  uneven,  splintery  or  conchoidal  fracture. 
It  is  usually  light  in  color.      Quartzite  has  been  derived  from 
a  sandstone  by  intense  metamorphism.     It  is  a  common  and 
widely  distributed  rock. 

4.  Slate.     Slates  are   exceedingly  fine-grained  rocks  which 
have  a  remarkable  cleavage  which  permits  them  to  be  split  into 
thin  and  broad  sheets.     Their  color  is  commonly  gray  to  black, 
but  may  be  green,  yellow,  brown,  red,  etc.     They  have  been 
formed    commonly   by   the   metamorphism    of   shales.     Their 
characteristic  slaty  cleavage  may  or  may  not  be  parallel  to  the 
bedding  planes  of  the  original  shales.     They  are  quite  common 
in  occurrence. 

5.  Various  Schists.   There  are  various  other  kinds  of  schistose 
rocks,  which  are  chiefly  derived  by  the  metamorphism  of  the 
ferromagnesian  igneous  rocks.    The  most  important  types  are 


THE  COMMON  ROCK-MAKING  MINERALS      339 

talc-schist,  chlorite-schist,  amphibolite  or  hornblende-schist.  They 
each  are  characterized,  as  their  names  indicate,  by  the  prepon- 
derance of  some  metamorphic  ferromagnesian  mineral. 

6.  Marble.  A  marble  is  a  metamorphosed  limestone.  It  is 
a  crystalline  rock  composed  of  grains  of  calcite,  or  more  rarely 
dolomite.  At  times  the  individual  grains  are  so  small  that  they 
cannot  be  distinguished  by  the  eye,  and  again  they  may  be  quite 
coarse  and  show  clearly  the  characteristic  cleavage  of  the  min- 
eral. Like  limestone,  a  marble  is  characterized  by  its  softness 
and  its  effervescence  with  acids.  When  pure,  marble  is  white  in 
color,  but  it  may  show  a  wide  range  of  color,  due  to  various  im- 
purities that  it  contains.  It  is  a  rock  which  is  found  in  many 
localities  and  at  times  in  thick  and  extensive  beds. 


The  Common  Rock-making  Minerals. 

Although  many  minerals  are  found  as  rock  constituents,  those 
which  can  be  termed  common  and  characteristic  rock-making 
minerals  are  comparatively  few  in  number.  The  following  list 
gives  the  names  of  these  minerals,  with  a  brief  statement  in  each 
case  of  the  types  of  rocks  in  which,  they  most  commonly  occur. 

1.  Quartz.     Quartz,  Si02,  is  a  very  common  and  widely  dis- 
tributed rock-making  mineral.     It  is  found  in  all  the  light- 
colored,  acid,  igneous  and  metamorphic  rocks.     It  is  the  chief 
constituent  of  sandstones  and  quartzites.     It  is  to  be  recognized 
by  its  hardness  (7),  its  vitreous  luster,  lack  of  cleavage  and  con- 
choidal  fracture.     When  it  occurs  in  igneous  rocks  it  often  has 
a  gray  or  smoky  color. 

2.  The   Feldspars.     The  feldspars   include   orthoclase   and 
microcline,  KAlSi308,  albite,  NaAlSi308,  anorthite,  CaAl2Si208, 
and  various  mixtures  of  these  last  two  as  oligoclase  (3  albite  to 
1  anorthite),  andesite  (1  albite  to  1  anorthite)  and  labradorite 
(1  albite  to  3  anorthite).    They  are  very  common  rock-making 
minerals  and  are  found  in  a  great  variety  of  rock  types.     They 
are  characteristic  of  most  igneous  rocks,  and  frequently  con- 
stitute a  large  proportion  of  them.     They  are  found  in  the 
gneisses  and  to  a  less  extent  in  some  sandstones.    They  are  to 


340  MANUAL  OF  MINERALOGY 

be  distinguished  by  their  two  cleavages  at  right  angles  or  nearly 
so,  their  vitreous  luster  and  their  hardness  (6).  It  frequently 
is  difficult,  if  not  impossible,  to  tell  the  kind  of  feldspar  present 
in  a  rock  by  inspection  alone.  Under  favorable  conditions 
twinning  striations  may  be  observed  on  the  best  cleavage  face, 
which  would  indicate  that  the  feldspar  belonged  to  the  plagio- 
clase  group  (see  page  225)  and  could  not  be  orthoclase. 

3.  Nephelite.     Nephelite  is  a  silicate  whose  composition  is 
essentially  NaAlSi04.     It  is  restricted  in  its  occurrence,  being 
found  only  in  certain  igneous  rocks,  such  as  the  nephelite  sye- 
nites, which  are  low  in  percentages  of  silica.     It  is  often  mistaken 
for  quartz,  but  the  two  minerals  are  practically  never  found  to- 
gether.    It  is  best  determined  by  a  chemical  test.     Unlike  most 
rock-making  minerals,  it  is  readily  soluble  in  hydrochloric  acid 
and  the  solution  gelatinizes  on  evaporation. 

4.  Sodalite.     Sodalite,  Na4(AlCl)Al2(Si04)3,  is  similar  in  its 
occurrence  to  nephelite,  with  which  it  is  commonly  associated. 
It  may  be  greenish  gray  or  white  in  color,  but  is  usually  blue. 
Haiiynite  and  noselite  are  similar  but  rare  species  which  occur 
in  the  same  way. 

5.  Leucite.     Leucite  has  the  composition  KAl(Si03)2.     It  is 
a  rare  rock-making  mineral  found  chiefly  in  rather  basic  lavas. 
It  is  commonly  in  the  form  of  phenocrysts  which  show  trape- 
zohedral  forms.     It  is  white  to  gray  in  color  with  a  dull  vitreous 
luster. 

6.  The  Micas.     The  micas  are  common  rock-making  min- 
erals.    They  may  be  divided  into  two  classes :  the  light  colored 
micas  which  are  chiefly  muscovite,  and  the  dark  colored  micas 
consisting  mostly  of  biotite.     They  are  to  be  determined  by 
their  micaceous  structure,  eminent  cleavage  and  the  elasticity 
of  their  leaves.     Muscovite  is  found  in  granites  and  syenites 
and  other  igneous  rocks.     It  is  especially  common  in  the  meta- 
morphic  rocks,  particularly  the  gneisses  and  schists.     Biotite  is 
found  in  many  igneous  rocks  such  as  the  granites,  syenites  and 
felsites.     It  occurs  also  in  the  gneisses  and  schists. 

7.  The  Pyroxenes.     The  pyroxenes  form  an  important  series 
of  rock-making  minerals  which,  although  the  different  members 


THE  COMMON  ROCK-MAKING  MINERALS      341 

vary  considerably  in  composition,  are  closely  related  crystallo- 
graphically.  The  important  types  are  hypersthene,  (Mg,Fe)Si03, 
diopside,  CaMg(Si03)2,  common  pyroxene,  Ca(Mg,Fe)(Si03)2, 
augite,  Ca(Mg,Fe)(Si03)2  with  (Mg,Fe)(Al,Fe)2Si06  as  well,  and 
segirite,  NaFe(Si03)2.  The  pyroxenes  are  characteristically 
found  in  igneous  rocks,  particularly  those  that  contain  large 
amounts  of  lime,  iron  and  magnesia,  such  as  basalt,  gabbro, 
peridotite,  etc.  Diopside  and  common  pyroxene  are  at  times 
found  in  metamorphic  limestones.  The  pyroxenes  vary  in  color 
from  white  through  green  to  black.  They  occur  usually  in 
small  grains  or  in  short  prisms.  If  they  show  distinct  crystal 
outlines,  they  can  be  told  by  the  square  cross  section  of  their 
prisms.  They  have  a  rather  poor  cleavage. 

8.  The  Amphiboles.      The  amphiboles  or  hornblendes  are 
calcium,  magnesium,  iron  metasilicates  which  closely  resemble 
the  pyroxenes  in  their  chemical  composition.    The  most  im- 
portant members  of  the  group  are  tremolite,  CaMg3(Si03)4, 
actinolite,  Ca(Mg,Fe)3(Si03)4,  common  hornblende,  Ca(Mg,Fe)3 
(Si03)4,  with  a  molecule  containing  aluminium  and  ferric  iron 
besides,  and  arfvedsonite,  which  contains  chiefly  soda,  lime  and 
iron  protoxide.     The  amphiboles  are  particularly  characteristic 
of  the  metamorphic  rocks,  but  are  found  in  the  igneous  rocks  as 
well.    Tremolite  is  most  commonly  found  in  crystalline  meta- 
morphosed   limestones,    actinolite    in    schists,    hornblende    in 
granites,  syenites  and  diorites,  and  also  in  gneisses  and  horn- 
blende schists.     The  amphiboles  commonly  occur  in  bladed 
prismatic  crystals  with  a  good  prismatic  cleavage.     The  cleav- 
age angle  is  broad,  having  a  value  of  about  125°.     They  vary 
in  color  from  white  through  green  to  black,   but  are  most 
commonly  green. 

9.  Chrysolite,  or  Olivine.     Chrysolite,  or  olivine,  as  it  is  more 
commonly  termed  when  spoken  of  as  a  rock  constituent,  is  an 
orthosilicate  of  magnesium  and  ferrous  iron  (Mg,Fe)2Si04.     It  is 
a  characteristic  constituent  of  the  ferromagnesian  igneous  rocks 
such  as  gabbros,  peridotites  and  basalts.     It  is  almost  the  only 
mineral  present  in  the  igneous  rock  known  as  dunite.    It  is  usually 
green  in  color,  with  a  vitreous  luster  and  granular  structure. 


342  MANUAL  OF  MINERALOGY 

10.  Kaolin.     Kaolin  is  a  silicate  of  aluminium,  H4Al2Si209, 
which  is  always  secondary  in  its  origin.     It  is  formed  by  the 
weathering  of  some  aluminium  silicate,  usually  a  feldspar.     It 
may  occur  in  quite  pure  masses  where  feldspathic  rocks  have 
been  entirely  altered,  but  is  most  commonly  found,  however,  in 
an  impure  state  in  clay,  and  in  the  rocks  formed  from  claylike 
materials  such  as  shales,  slates,  etc.     When  pure  it  is  often  friable 
or  mealy  in  structure,  although  at  times  it  is  compact.     It  varies 
in  color  from  white  to  yellow,  brown,  red,  etc.,  depending  upon 
the  amount  and  character  of  the  foreign  material  mixed  with  it. 

11.  Chlorites.    The  chlorites  are  a  group  of  green-colored 
micaceous  minerals  of  which  clinochlore  is  the  most  common 
member.     In  composition  they  are  hydrous  silicates  of  alumin- 
ium  and   magnesium.     They   are  always   secondary   in   their 
origin.     They  are  frequently  formed  by  the  alteration  of  the 
ferromagnesian  minerals  occurring  in  igneous  rocks.     The  green 
color  of  such  rocks  is  usually  due  to  the  presence  of  chlorite. 
They  are  also  common  in  the  chlorite-schists,  in  green  slates,  etc. 
They  are  to  be  recognized  by  their  green  color,  micaceous  structure, 
perfect  cleavage,  and  by  the  fact  that  their  leaves  are  not  elastic. 

12.  Serpentine.     Serpentine,  H4Mg3Si209,  is  also  a  secondary 
mineral  formed  by  the  alteration  of  some  original  ferromagnesian 
mineral,  such  as  pyroxene,  amphibole,  and  especially  olivine.    It 
occurs,  therefore,  in  altered  igneous  rocks  and  in  metamorphic 
rocks.     It  may  occur  in  disseminated  particles  or  in  rock  masses, 
of  which  it  is  the  chief  mineral.     It  is  usually  of  some  shade  of 
green  in  color  and  has  an  oily  or  waxy  luster.     It  is  usually  mas- 
sive in  structure,  but  may  become  coarsely  fibrous  in  the  variety 
known  as  chrysotile. 

13.  Talc.     Talc,  H2Mg3(Si03)4,  is  similar  in  its  origin  and  oc- 
currence to  serpentine.     It  is  found  at  times  in  altered  igneous 
rocks,  but  is  more  characteristic  of  metamorphic  rocks  where 
it  may  occur  in  large  beds  as  soapstone.     It  is  characterized 
by  its  extreme  softness  (1),  greasy  feel  and  also  frequently  by 
its  foliated  structure. 

14.  Calcite.     Calcite,  CaC03,  is  a  common  and  widely  dis- 
tributed rock-making  mineral  found  chiefly  in  the  sedimentary 


ACCESSORY  ROCK-MAKING  MINERALS      343 

and  metamorphic  rocks.  Such  rocks  as  the  limestones,  marbles 
and  chalks  are  composed  almost  entirely  of  the  mineral.  It  is 
to  be  told  by  its  softness  (3),  its  rhombohedral  cleavage  and  its 
ready  effervescence  in  cold  acids. 

15.  Dolomite.  Dolomite,  CaMg(C03)2,  is  found  in  the  same 
way  as  calcite  but  less  commonly.  The  two  minerals  are  usually 
associated  with  each  other  and  form  dolomite  marbles  and 
dolomitic  limestones.  Its  physical  properties  are  practically 
the  same  as  those  of  calcite.  It  will  only  effervesce,  however, 
in  hot  acids. 

Accessory  Rock-making  Minerals. 

In  addition  to  the  more  important  and  common  rock-making 
minerals  that  have  been  described  in  the  preceding  pages,  there 
is  a  group  of  minerals  which  are  characteristically  found  as  rock 
constituents  but  in  a  minor  way.  They  occur  usually  only  as 
small  and  scattered  crystals  in  the  rock  and  seldom  become  one 
of  its  prime  constituents.  These  minerals  are  known  as  acces- 
sory rock-making  minerals.  The  occurrences  of  the  more  im- 
portant of  them  are  briefly  described  below. 

1.  Garnet.     Garnet  is  a  common  accessory  mineral,  being  par- 
ticularly characteristic  of  the  metamorphic  rocks.     It  is  found 
frequently  in  mica-schists,  hornblende-schists,  gneisses  and  meta- 
morphosed limestones.     More  rarely  it  is  found  in  igneous  rocks. 
It   occurs  in  small  irregular  grains  or  frequently  in  fair-sized 
definitely  shaped  crystals.     It  is  usually  red  or  brown  in  color. 
For  the  different  varieties  of  garnets  and  their  distinguishing 
features,  see  p.  245. 

2.  Epidote.     Epidote  is  formed  by  the  alteration  of  silicates 
containing  lime,  iron  and  aluminium.     It  is  also  characteristic 
of   metamorphosed   limestones.     It   may   be   associated   with 
chlorite,  calcite,  etc.     It  is  usually  found  in  bladed  crystalline 
masses  and  has  a  characteristic  yellow-green  color,  is  hard  and 
has  one  good  cleavage. 

3.  Staurolite.     Staurolite  is  found  in  metamorphic  rocks,  such 
as  the  mica-schists  and  slates.     Sometimes  it  is  a  constituent  of 
gneiss.     It  is  associated  with  mica,  quartz,  garnet,  cyanite,  etc 


344  MANUAL  OF  MINERALOGY 

It  is  characterized  by  a  brown  color,  hardness  (7)  and  prismatic 
orthorhombic  crystals  which  may  show  cross-shaped  twins. 

4.  Cyanite.     Cyanite,  Al2Si05,  is  a  rather  rare  accessory  min- 
eral which  is  found  in  gneisses  and  mica-schists.     It  is  associated 
with  muscovite,  quartz,  garnet,  staurolite,  etc.     It  is  to  be  dis- 
tinguished by  its  bladed  structure,  one  good  cleavage,  blue  color 
and  by  the  fact  that  it  is  distinctly  harder  in  the  direction  parallel 
to  the  length  of  the  crystals  than  in  the  direction  at  right  angles 
to  this. 

5.  Zircon.     Zircon,  ZrSi04,  is  a  rather  rare  mineral  which 
usually  occurs  in  minute  crystals  scattered  throughout  a  rock 
mass.     It  is  found  in  granites,  syenites,  crystalline  limestones, 
chloritic  schists,  etc.     It  is  to  be  distinguished  by  its  usually 
brown  color,  hardness  (7.5)  and  tetragonal  crystallization. 

6.  Titanite.     Titanite  or  sphene,  CaTiSi05,  is  a  compara- 
tively rare  mineral  found  as  an  accessory  constituent  in  granite, 
syenites,  gneiss,  mica-  and  chlorite-schists  and  crystalline  lime- 
stones.    It  occurs  as  microscopical  crystals  in  many  igneous 
rocks. 

7.  Magnetite.     Magnetite,  Fe3()4,  is  widespread  in  its  occur- 
rence as  a  rock  constituent.     It  is  found  in  all  kinds  of  igneous 
rocks,  usually  in  small  disseminated  grains.     It  is  also  charac- 
teristic of  the  crystalline  schists  and  gneisses.     Ordinarily  it 
occurs  in  comparatively  small  amounts  and  would  be  classed  as 
an  accessory  mineral  but  at  times  it  becomes  a  prime  constituent 
of  the  rock  and  may  be  segregated  into  almost  pure  bodies  of 
the  mineral.     It  is  characterized  by  its  metallic  luster,  black 
color  and  streak  and  its  strong  magnetic  properties. 

8.  Ilmenite.     Ilmenite  or  titanic  iron,  FeTi03,  is  a  common 
accessory  mineral  occurring  in  the  same  way  as  magnetite  and 
frequently  found  associated  with  it.     It  is  most  commonly  found 
in  the  gabbros  and  related  rocks.     It  is  difficult  to  tell  it  frpm 
magnetite  by  simple  inspection. 

9.  Hematite.     Hematite,  Fe203,  is  found  as  an  accessory  min- 
eral in  the  feldspathic  igneous  rocks  such  as  granite.     It  occurs 
also  in  the  crystalline  schists.     It  is  common  in  the  sedimentary 
and  metamorphic  rocks  and  at  times  forms  large  bodies  of  almost 


PEGMATITE  DIKES  AND   VEINS  345 

pure  mineral.  It  is  the  red  pigment  in  many  rocks  and  soils 
and  forms  the  cementing  material  in  many  sandstones.  It  is 
to  be  recognized  by  its  red  streak. 

10.  Pyrite.     Pyrite,  FeS2,  is  found  in  small  disseminated  crys- 
tals in  all  classes  of  rocks.     It  is  characterized  by  its  pale  brass 
color,  metallic  luster,  hardness  (6),  black  streak  and  frequently 
also  by  its  isometric  crystal  forms. 

11.  Apatite.     Apatite,  Ca4(CaF)(P04)3,  is  found  in  crystals  of 
considerable  size  in  metamorphosed  limestones.     It  is  also  com- 
mon in  microscopic  crystals  in  all  varieties  of  igneous  rocks,  and 
in  many  metamorphic  ones. 

In  addition  to  the  minerals  listed  above,  the  following,  more 
rare  in  their  occurrence,  are  at  times  found -as  accessory  rock 
constituents;  rutile,  iolite,  scapolite,  andalusite  and  sillimamte. 

Pegmatite  Dikes  and  Veins. 

In  connection  with  the  deep-seated,  coarse-grained  igneous 
rocks,  especially  the  granites,  we  frequently  find*' mineral  de- 
posits which  are  known  as  pegmatite  dikes  or  veins.  These 
bodies  have  the  general  shape  and  character  of  an  igneous  dike 
or  a  broad  mineral  vein  although  in  certain  respects  they  differ 
markedly  from  either  of  these.  They  are  to  be  found  running 
through  the  main  mass  of  the  igneous  rock  or  filling  fissures  in 
the  other  surrounding  rocks.  They  are  composed  chiefly  of 
the  same  minerals  as  occur  in  the  igneous  rock,  but  usually  in 
very  coarse  crystallizations.  A  granite  pegmatite  is  therefore 
made  up  principally  of  quartz,  feldspar  and  mica.  The  quartz 
and  feldspar  crystals  may  be  several  feet  in  length  and  the  mica 
plates  are  at  times  more  than  a  foot  across.  In  addition  to  the 
coarseness  of  the  crystallization  of  the  minerals,  these  veins 
possess  other  peculiar  features.  The  minerals  of  a  pegmatite 
vein,  for  instance,  have  not  apparently  been  deposited  in  the 
definite  order  that  prevailed  in  the  igneous  rock  mass,  but  their 
crystals  have  grown  more  nearly  simultaneously.  These  veins 
will  also  at  times  show  a  ribboned  or  banded  structure  where 
the  different  minerals  occur  in  distinct  layers  which  lie  parallel 


346  MANUAL  OF  MINERALOGY 

to  the  walls  of  the  deposit.  Their  minerals  are  also  commonly 
quite  irregularly  distributed  through  the  mass,  so  that  at  times 
the  vein  is  composed  chiefly  of  feldspar  and  again  becomes  nearly 
pure  quartz.  Frequently,  along  the  central  portion  of  the  dike, 
cavities  and  openings  will  be  observed  into  which  crystals  of 
the  different  minerals  project.  These  characteristics  point  to 
a  somewhat  different  origin  for  the  pegmatite  veins  from  that 
of  the  igneous  rock  with  which  they  are  associated. 

No  extended  and  detailed  discussion  of  the  theory  of  the  origin 
of  pegmatite  veins  can  be  given  here,  but  it  may  be  briefly  sum- 
marized as  follows.  Pegmatite  veins  are  formed  during  the 
last  stages  of  the  cooling  and  solidification  of  a  plutonic  igneous 
rock.  As  an  igneous  magma  cools  and  slowly  solidifies,  it  shrinks 
somewhat  in  volume  and  various  cracks  and  fissures  open  up 
throughout  the  mass.  The  pressure  due  to  the  weight  of  the 
rock  forces  any  still  fluid  material  from  the  interior  of  the  mass 
up  through  these  cracks  and  also  into  any  fissures  that  may  exist 
in  the  surrounding  rocks.  The  filling  up  of  these  fissures  both 
in  the  igneous  rock  itself  and  in  the  neighboring  rocks  consti- 
tutes a  pegmatite  vein.  As  a  magma  cools  and  its  minerals 
crystallize,  large  amounts  of  water  vapor  are  frequently  set  free 
so  that  the  residue  of  the  still  fused  rock  material  must  contain 
much  higher  percentages  of  water  than  the  original  magma. 
Consequently  it  becomes  in  its  character  and  behavior  more 
like  a  solution  than  a  fused  mass.  This  would  account  for  the 
peculiar  features  observed  in  pegmatite  veins  which  differentiate 
them  from  ordinary  igneous  deposits. 

The  minerals  found  in  pegmatite  veins  may  be  divided  into 
three  general  divisions.  '  First  come  those  minerals  which  form 
the  main  mass  of  the  deposit  and  which,  as  stated  above,  are  the 
same  as  the  prominent  minerals  of  the  igneous  rock  with  which 
the  pegmatite  dike  is  associated.  These  are  commonly  quartz, 
a  feldspar  which  is  usually  either  orthoclase  or  microdine,  but 
may  be  albite,  and  a  mica  which  may  "be  either  muscovite  or 
bidtite.  Garnet  is  also  at  times  in  a  smaller  way  a  characteristic 
constituent.  Second  comes  a  series  of  rare  minerals  which  are, 
however,  quite  commonly  observed  in  pegmatite  deposits,  and 


CONTACT  METAMORPHIC  MINERALS  347 

which  are  characterized  by  the  presence  in  them  of  fluorine, 
boron  or  hydroxyl.  Their  presence  in  the  veins  indicates  also 
that  gases  under  high  pressures  have  been  instrumental  in  their 
formation.  The  minerals  of  this  type  include  beryl,  tourmaline, 
apatite  &ndfluorite.  A  third  class  of  minerals  found  in  pegmatite 
veins  includes  species  containing  rare  elements  such  as  lithium, 
molybdenum,  tin,  niobium  and  tantalum,  the  rare  earths,  etc. 
These  are  minerals  which  are  rarer  still  in  their  occurrence,  but 
when  they  do  occur  are  usually  to  be  found  in  pegmatite  deposits. 
The  most  important  members  of  this  group  are  molybdenite, 
lepidolite,  spodumene,  triphylite,  columbite,  cassiterite  and'monazite. 
Because  of  the  frequent  occurrence  in  pegmatite  veins  of  the 
rare  minerals  mentioned  above,  some  of  which  are  often  found 
finely  colored  and  well  crystallized,  these  deposits  are  of  particu- 
lar interest  to  students  of  mineralogy.  Pegmatite  veins  are  also 
of  commercial  importance,  for  it  is  from  them  that  most  of  the 
feldspar  and  mica  used  in' the  arts  are  obtained.  Many  beautiful 
gem  stones,  such  as  beryl  and  tourmaline,  are  also  found  in  them. 
Pegmatite  veins  are  widely  distributed  in  their  occurrence,  being 
almost  universally  found  wherever  plutonic  igneous  rocks  are 
exposed.  Important  districts  for  pegmatite  veins  in  the  United 
States  include  the  New  England  states,  the  Black  Hills  in  South 
Dakota  and  Southern  California. 

Contact  Metamorphic  Minerals. 

When  an  igneous  rock  magma  is  intruded  into  the  earth's  crust, 
it  causes  through  the  attendant  heat  and  pressure  a  greater  or 
less  alteration  in  the  surrounding  rock.  This  alteration,  or 
rnetamorphism,  of  the  rocks  lying  next  to  an  igneous  intrusion 
usually  consists  partly  in  the  development  of  new  and  charac- 
teristic mineral  species.  The  minerals  that  are  formed  under 
these  conditions  are  known  as  contact  metamorphic  minerals, 
since  they  are  produced  by  a  metamorphic  change  and  are  to 
be  found  at  or  near  the  contact  line  between  the  rock  in  which 
they  lie  and  an  igneous  rock.  Any  rock  into  which  an  igneous 
mass  is  intruded  will  be  affected  in  a  greater  or  less  degree,  the 


348  MANUAL  OF  MINERALOGY 

amount  and  character  of  the  change  depending  chiefly  upon  the 
size  of  the  intruded  mass  and  upon  the  chemical  and  physical 
character  of  the  surrounding  rock.  The  most  striking  and  im- 
portant contact  metamorphic  changes  take  place  when  the 
igneous  rock  is  intruded  into  impure  limestones.  When,  a  pure 
limestone  is  affected,  it  is  recrystallized  and  converted  into  a 
marble,  but  without  any  development  of  new  species.  But,  on 
the  other  hand,  in  the  case  of  an  impure  limestone  the  heat  and 
pressure  caused  by  the  igneous  intrusion  will  serve  to  develop 
new  and  characteristic  minerals  in  the  rock.  An  impure  lime- 
stone will  ordinarily  contain,  besides  the  calcium  carbonate  of  the 
rock,  varying  amounts  of  quartz,  clay,  iron  oxide,  etc.  Under 
the  influence  of  the  heat  and  pressure  these  materials  will  com- 
bine with  the  calcium  carbonate  to  form  new  minerals.  For 
instance,  the  calcite  and  quartz  may  react  together  to  form 
wollastonite,  CaSi03.  If  the  limestone  contains  dolomite,  the 
reaction  of  this  mineral  with  quartz '  may  produce  pyroxene, 
(Ca,Mg)Si03.  If  clay  is  present,  aluminium  will  enter  into  the 
reaction  and  such  minerals  as  spinel,  MgAl204,  and  grossularite, 
Ca3Al2Si3Oi2,  may  result.  If  any  carbonaceous  materials  are 
present,  the  effect  of  the  metamorphism  may  convert  them  into 
graphite.  The  common  contact  metamorphic  minerals  found 
in  limestone  are  as  follows:  graphite,  spinel,  corundum,  wollas- 
tonite, tremolite,  pyroxene  and  the  lime  garnets,  grossularite  and 
andradite. 

As  mentioned  in  a  preceding  paragraph,  an  igneous  rock  in 
cooling  often  gives  off  large  amounts  of  mineralizing  vapors. 
These  consist  largely  of  water  vapor,  but  often  include  boron 
and  fluorine  gases.  Under  the  influence  of  these  vapors,  other 
minerals  are  often  formed  in  the  contact  zone  of  a  limestone. 
These  particular  minerals  are  commonly  spoken  of  as  pneumato- 
lytic  minerals,  since  they  are  formed,  partly  at  least,  through  the 
agency  of  mineral  gases.  They  consist  chiefly  of  calcium  and 
aluminium  silicates  which  contain  hydroxyl,  fluorine  or  boron. 
The  most  common  of  the  pneumatolytic  contact  minerals  are 
chondrodite,  vesuvianite,  scapolite,  phlogopite,  tourmaline  and 
fluorite. 


VEINS  AND  VEIN  MINERALS  349 

Veins  and  Vein  Minerals. 

Most  of  the  important  mineral  deposits,  especially  those  that 
furnish  the  valuable  metals,  are  found  in  what  are  known  as 
veins.  A  brief  discussion  of  veins  and  vein  minerals  follows. 

The  rocks  of  the  earth's  crust  have  many  openings  existing 
within  them.  These  openings  vary  in  size  from  microscopic 
cracks  to  cavities  of  considerable  extent.  The  openings  may  be 
irregular  and  discontinuous  or  they  may  be  in  the  form  of  fissures 
which  are  continuous  for  greater  or  less  distances.  Below  a 
certain  inconsiderable  depth,  these  openings  are  largely  filled  by 
water.  This  underground  water,  as  it  is  termed,  slowly  circu- 
lates through  the  rocks  by  means  of  the  openings  in  them. 
Through  a  large  part  of  its  circulation,  the  water  must  exist  at  a 
high  temperature  and  pressure,  and  under  these  circumstances 
becomes  a  strong  solvent  and  active  chemical  agent.  Under- 
ground water  in  general  descends  slowly  through  the  smaller 
openings  in  the  rocks,  and  then  gradually  finding  its  way  into 
the  bigger  openings  will  at  last  enter  some  larger  fissure  and 
changing  its  course  will  begin  to  ascend.  On  its  passage  through 
the  rocks,  it  will  have  dissolved  their  more  soluble 'constituents, 
and  when  it  ultimately  enters  the  larger  fissures  and  commences 
to  rise  will  be  carrying  considerable  amounts  of  dissolved  mineral 
material.  The  igneous  rocks  in  particular  are  important  factors 
in  furnishing  underground  waters  with  mineral  constituents 
partly  because  of  the  <effect  of  their  heat  upon  its  activity,  and 
partly  because  they  give  off  in  the  form  of  vapors  a  large  amount 
of  mineral  material  which  ultimately  gets  into  the  underground 
circulation.  When  these  mineral  laden  waters  commence  to  rise 
in  the  larger  fissures,  they  slowly  come  into  regions  of  lower  pres- 
sure and  temperature.  Under  these  changing  conditions,  the 
water  will  not  be  able  to  retain  all  its  mineral  constituents  in 
solution,  and  their  points  of  saturation  being  reached  various 
minerals  will  begin  to  crystallize  out  and  be  deposited  on  the  walls 
of  the  fissure.  In  time,  if  the  process  continues,  the  fissure  may 
be  completely  filled  from  wall  to  wall  with  minerals  deposited 
in  this  way.  Such  a  filled  fissure  is  known  as  a  mineral  vein. 


350  MANUAL  OF  MINERALOGY 

Evidence  tha.t  the  minerals  of  a  vein  have  been  deposited  from 
solution  is  given  by  the  following  facts.  Often  a  mineral  vein 
shows  a  distinctly  banded  or  ribboned  structure.  That  is,  the 
different  minerals  occur  in  more  or  less  regular  layers  which  lie 
parallel  to  the  walls.  This  shows  that  the  various  minerals  have 
not  been  deposited  simultaneously,  but  in  a  definite  order  of 
succession.  Again,  frequently  it  will  be  observed  that  the  vein 
material  has  not  completely  filled  the  fissure,  but  that  there  are 
openings  left  along  its  central  line.  These  openings  are  termed 
vugs  and  are  often  lined  with  crystallized  minerals.  These  con- 
ditions cannot  be  easily  explained  except  on  the  assumption  that 
the  contents  of  a  mineral  vein  have  been  deposited  from  solution. 

The  shape  and  general  physical  character  of  a  vein  depends 
upon  the  type  of  fissure  its  minerals  have  been  deposited  in,  and 
the  type  of  fissure  in  turn  depends  upon  the  character  of  the  rock 
in  which  it  lies  and  the  kind  of  force  which  originally  caused  its 
formation.  In  a  firm  homogeneous  rock,  like  a  granite,  a  fissure 
will  be  fairly  regular  and  clean  cut  in  character.  It  is  liable  to 
be  comparatively  narrow  in  respect  to  its  horizontal  and  vertical 
extent  and  reasonably  straight  in  its  course.  On  the  other  hand, 
if  a  rock  that  is  easily  fractured  and  splintered,  like  a  slate  or 
a  schist,  is  subjected  to  a  breaking  strain,  we  are  more  liable  to 
have  formed  a  zone  of  narrow  and  interlacing  fissures,  rather 
than  one  straight  crack.  In  an  easily  soluble  rock  like  a  lime- 
stone, a  fissure  will  often  be  extremely  irregular  in  its  shape  and 
size  due  more  or  less  to  a  solution  of  its  walls  by  the  waters  that 
have  flowed  through  it. 

A  typical  vein  consists  of  a  mineral  deposit  which  has  filled  a 
fissure  solidly  from  wall  to  wall,  and  shows  sharply  defined 
boundaries.  There  are,  however,  many  variations  from  this 
type.  Frequently,  as  observed  above,  irregular  openings  termed 
vugs  may  occur  among  the  vein  minerals.  It  is  from  these  vugs 
that  we  obtain  many  of  our  crystallized  mineral  specimens. 
Again,  the  walls  of  a  vein  may  not  be  sharply  defined.  The  min- 
eralizing waters  that  filled  the  fissure  may  have  acted  upon  the 
wall  rocks  and  partially  dissolving  them  may  have  replaced  them 
with  the  vein  minerals.  Consequently  we  may  have  almost  a 


VEINS  AND   VEIN  MINERALS  351 

complete  gradation  from  the  unaltered  rock  to  the  pure  vein 
filling,  and  with  no  sharp  line  of  division  between.  Some  de- 
posits have  been  largely  formed  by  the  deposition  of  vein  min- 
erals in  the  wall  rocks.  Such  deposits  are  known  as  replacement 
deposits.  They  are  more  liable  to  be  found  in  the  soluble  rocks 
like  limestones.  There  is  every  gradation  possible  from  a  true 
vein  with  sharply  defined  walls  to  a  replacement  deposit  with 
indefinite  boundaries. 

The  mineral  contents  of  a  vein  depend  chiefly  upon  the  chemi- 
cal composition  of  the  waters  from  which  its  minerals  have 
crystallized.  There  are  many  different  sorts  of  veins,  and  many 
different  mineral  associations  are  observed  in  them.  There  are, 
however,  certain  minerals  and  associations  that  are  more  frequent 
in  their  occurrence  to  which  attention  should  be  drawn.  The 
sulphides  form  perhaps,  the  most  characteristic  chemical  group 
of  minerals  to  be  found  in  veins.  The  following  minerals  are 
very  common  vein  minerals,  pyrite,  FeS2,  chalcopyrite,  CuFeS2, 
galena,  PbS,  sphalerite,  ZnS,  chalcocite,  Cu2S,  bornite,  Cu5FeS4, 
marcasite,  FeS2,  arsenopyrite,  FeAsS,  stibnite,  Sb2S3,  tetrahedrite, 
Cu8Sb2S7,  etc.  In  addition  to  these,  which  in  large  part  com- 
prise our  ore  minerals,  certain  nonmetallic  minerals  are  also 
commonly  to  be  observed.  These  being  of  no  particular  com- 
mercial value  are  called  gangue  minerals  (gangue  is  from  gang, 
a  vein) .  They  include  the  following :  quartz,  Si02,  cakite,  CaC03, 
dolomite,  CaMg(C03)2,  siderite,  FeC03,  barite,  BaS04,  fluorite, 
CaF2,  rhodochrosite,  MnC03,  etc. 

While  comparatively  few  positive  statements  concerning  the 
associations  of  vein  minerals  can  be  made,  the  following  points 
are  of  interest. 

1.  Gold-bearing  Quartz  Veins.     Native  gold  is  most  com- 
monly found  in  quartz  veins.     It  may  occur  alone  in  the  quartz 
either  in  nests  or  in  finely  disseminated  particles,  or  it  may 
occur  in  connection  with  certain  sulphides  in  the  veins.    The 
most  common  sulphides  found  in  such  connections  are  pyrite, 
chalcopyrite  and  arsenopyrite. 

2.  Gold-  and  Silver-bearing  Copper  Veins.     The  gold  and 
silver  content  of  these  veins  is  associated  with  the  various  copper 


352  MANUAL  OF  MINERALOGY 

sulphides.  Frequently  the  amount  of  the  precious  metals  is 
quite  small.  The  chief  minerals  'are  chalcopyrite,  tetrahedrite, 
bornite,  chalcocite,  pyrite  and  various  rarer  silver  minerals. 

3.  Silver-bearing  Lead  Veins.     Silver  and  lead  minerals  are 
very  commonly  associated  with  each  other.     These  veins  contain 
such  minerals  as  galena,  argentite,  tetrahedrite,  sphalerite,  pyrite, 
calcite,  dolomite,  rhodochrosite,  etc. 

4.  Lead-zinc  Veins.     Lead  and  zinc  minerals  often  occur  to- 
gether particularly  in  deposits  that  lie  in  limestones.     The  chief 
minerals   of  such  deposits   are  galena,   sphalerite,   marcasite, 
chalcopyrite,  smithsonite,  calamine,  cerussite,  calcite,  dolomite. 

5.  Copper-iron  Veins.     Copper  and  iron  sulphides  are  quite 
commonly  associated  with  each  other,  the  prominent  minerals 
of  such  veins  being  pyrite,   chalcopyrite,  chalcocite,   bornite, 
tetrahedrite,  enargite,  etc. 

Primary  and  Secondary  Vein  Minerals.    Secondary 
Enrichment. 

In  many  mineral  veins,  it  is  obvious  that  certain  minerals 
belong  to  the  original  vein  deposit  while  certain  others  have  been 
formed  subsequently.  These  two  classes  of  minerals  are  known 
respectively  as  Primary  and  Secondary  Minerals.  The  primary 
vein  minerals  are  those  which  were  originally  deposited  by  the 
ascending  waters  in  the  vein  fissure.  The  primary  metallic  vein 
minerals  are  comparatively  few  in  number,  the  more  important 
being  pyrite,  chalcopyrite,  galena  and  sphalerite.  The  second- 
ary vein  minerals  have  been  formed  from  the  primary  minerals 
by  some  subsequent  chemical  reaction.  This  change  is  ordi- 
narily brought  about  through  the  influence  of  oxidizing  waters 
which  coming  from  the  surface  of  the  earth  descend  through  the 
upper  portions  of  the  vein.  Under  these  conditions,  various  new 
minerals  are  formed,  many  of  them  being  oxidized  compounds. 
As  the  descending  waters  lose  their  oxygen  content  within  a 
comparatively  short  distance  of  the  earth's  surface,  the  secondary 
minerals  are  only  to  be  found  in  the  upper  part  of  a  vein.  To- 
gether with  the  formation  of  these  secondary  minerals,  there  is 


VEIN  MINERALS  353 

frequently  a  downward  migration  of  the  valuable  metals  in  the 
vein.  This  is  brought  about  by  the  solution  of  the  minerals  in 
the  uppermost  portion  of  the  vein  and  a  subsequent  reprecipi- 
tation  a  little  farther  down.  As  the  surface  of  the  earth  is 
gradually  lowered  by  erosion,  the  upper  part  of  a  vein  is  con- 
tinually being  worn  away.  But  the  metallic  content  of  the 
uppermost  part  of  the  vein  is  always  being  carried  downward 
by  the  descending  oxidizing  waters.  In  this  way,  the  metallic 
content  of  the  upper  part  of  many  veins  has  been  notably  en- 
riched since  there  is  concentrated  in  this  short  space  most  of  the 
original  contents  of  hundreds,  perhaps  thousands,  of  feet  of  the 
vein  which  have  been  slowly  worn  away  by  the  general  erosion 
of  the  country.  Consequently  the  zone  of  the  secondary  vein 
minerals  is  also  frequently  a  zone  of  secondary  enrichment. 
This  is  an  important  fact  to  be  borne  in  mind  since,  because  of 
it,  the  upper  two  or  three  hundred  feet  of  a  vein  are  ordinarily 
the  richest  portion  of  a  deposit.  The  ore  below  that  depth  grad- 
ually reverts  to  its  original  unaltered  and  unenriched  character 
and  may  frequently  prove  too  low  in  value  to  warrant  its  being 
mined.  The  prevalent  idea  that  the  ore  of  a  vein  must  increase 
in  value  with  increasing  depth  is  not  true  in  the  great  majority 
of  cases. 

It  will  be  of  interest  to  consider  the  more  important  primary 
vein  minerals  and  the  secondary  minerals  that  are  commonly 
formed  from  them. 

1.  Iron  Minerals.     The  common  primary  vein  iron  mineral  is 
pyrite,  FeS2.     Marcasite,  FeS2,  while  not  so  common  in  occur- 
rence is  also  a  primary  mineral.     When  oxidized,  these  minerals 
yield  ordinarily  the  hydrated  oxide  limonite,  Fe403[OH]6.     The 
upper  portion  of  a  vein  that  Was  originally  rich  in  pyrite  will 
often  show  a  cellular  and  rusty  mass  of  limonite.     This  limonite 
deposit  near  the  surface  is  commonly  termed  gossan.    The  yel- 
low rusty  character  of  the  outcrop  of  many  veins  enables  one 
frequently  to  locate  them  and  to  trace  them  across  the  country. 

2.  Copper  Minerals.     The  one  common  primary  copper  min- 
eral is  chalcopyrite,  CuFeS2.    At  times,  some  of  the  other  sul- 
phides may  be  primary  in  their  origin,  but  this  is  not  generally 


354  MANUAL  OF  MINERALOGY 

the  case.  The  secondary  formation  of  bornite  and  chalcocite 
may  be  explained  as  follows.  The  copper  sulphide  existing  in 
the  original  chalcopyrite  is  oxidized  by  the  descending  waters  at 
the  surface  to  copper  sulphate  which  is  then  dissolved  and  carried 
farther  down  the  vein.  Here  it  comes  in  contact  with  unaltered 
chalcopyrite  and  a  reaction  takes  place  which  enriches  the  sul- 
phide, changing  it  to  bornite,  Cu5FeS4.  Later,  more  copper 
sulphate  in  solution  comes  in  contact  with  the  bornite  and  a 
further  enrichment  takes  place  with  the  formation  of  chalcocite, 
Cu2S.  In  each  case,  there  is  an  interchange  of  metals,  the  iron 
in  the  original  sulphide  going  into  solution  as  a  sulphate  thus 
taking  the  place  of  the  copper  which  has  been  precipitated.  If 
the  copper  deposit  lies  in  limestone  rocks,  we  commonly  find  the 
various  carbonates  and  oxides  of  copper  also  formed  in  the  upper 
parts  of  the  deposit.  The  secondary  copper  minerals  therefore 
include  chalcocite ,  Cu2S,  bornite,  Cu5FeS4,  native  copper,  Cu,  cu- 
prite, Cu20,  malachite,  (Cu.OH)2C03,  azurite,  Cu(Cu.OH)2(CQ3)2, 
chrysocolla,  CuSi03.2H20,  chalcanthite,  CuS04.5H20. 

3.  Lead  Minerals.     The  one  primary  lead  mineral  is  galena, 
PbS.     The  secondary  minerals  of  lead  are  all  oxidized  compounds 
and  include  the  following:  cerussite,  PbC03,  anglesite,  PbS04, 
pyromorphite,  Pb4(PbCl)(P04)3,  wulfenite,  PbMo04. 

4.  Zinc  Minerals.    Sphalerite,  ZnS,  is  the  only  common  prim- 
ary zinc  mineral.     The  chief  secondary  minerals  are  smithsonite, 
ZnC03,  and  calamine,  H2(Zn20)Si04. 

5.  Silver  Minerals.     Probably  most  of  the  sulphide  minerals 
of  silver  are  primary  in  their  origin.     The  following  minerals  are 
usually  secondary,  although  native  silver  at  times  appears  pri- 
mary; native  silver,  Ag,  cerargyrite,  AgCl,  embolite,  Ag(Cl,Br),  etc. 

Lists  of  Minerals  Arranged  According  to  Systems 
of  Crystallization. 

In  the  following  tables  the  minerals  which  are  described  in  this 
book  are  listed  according  to  the  system  of  crystallization  to  which 
they  belong.  The  order  in  which  they  are  given  is  according  to 
the  chemical  classification  adopted  in  this  book. 


LISTS  OF  MINERALS 


355 


ISOMETRIC  SYSTEM:   NORMAL  CLASS. 
Elements. 


1.  Diamond,  C. 

2.  Gold,  Au. 

3.  Silver,  Ag. 


1.  Galena,  PbS. 

2.  Argentite,  Ag2S. 

3.  Pentlandite,  (Ni,Fe)S. 


4.  Copper,  Cu. 

5.  Platinum,  Pt. 

6.  Iron,  Fe. 


Sulphides. 

4.  Bornite,  Cu5FeS4. 

5.  Linnaeite,  Co3S4. 


1.  Halite,  NaCl. 

2.  Sylvite,  KC1. 

3.  Cerargyrite,  AgCl. 


Chlorides,  etc. 

4.  Embolite,  Ag(Cl,Br). 

5.  Fluorite,  CaF2. 


1.  Senarmontite,  Sb203. 

2.  Cuprite,  Cu20. 


Oxides. 

4.  Gahnite,  ZnAl204. 

5.  Magnetite,  Fe3O4. 


Spinel  Group,  R"R'"204 


or  R"O.R'"203. 
3.   Spinel,  MgAl204. 


6.  Franklinite,   (Fe,Mn,Zn) 

(Fe,  Mn)204. 

7.  Chromite,  (Fe,Mg)Cr204. 


Silicates. 


1.  Leucite,  KAl(Si03)2. 

2.  Analcite,NaAl(Si03)2.H20. 

3.  Sodalite, 

Na4(AlCl)Al2(Si04)3. 

4.  Lazurite, 

Na4(Al.NaS3)Al2(Si04)3. 


5.   Garnet  Group,  R3R2(Si04)3. 
Grossularite,  Ca3Al2(Si04)3. 
Pyrope,  Mg3Al2(Si04)3. 
Almandite,  Fe3Al2(Si04)3. 
Spessartite,  Mn3Al2(Si04)3. 
Andradite,  Ca3Fe2(Si04)3. 
Uvarovite, 
Ca3(Cr,Al)2(Si04)3. 


Uranate. 
1.   Uraninite,    U03    and    U02  with  Th,  Y,  Ce,  Pb,  He,  Ra. 


356  MANUAL  OF  MINERALOGY 

ISOMETRIC  SYSTEM:   PYRITOHEDRAL  CLASS. 
Sulphides,  etc. 


1.  Pyrite,FeS2. 

2.  Smaltite,  CoAs2. 

3.  Chloanthite,  NiAs2. 


4.  Cobaltite,  CoAsS. 

5.  Gersdorffite,  NiAsS. 

6.  Sperrylite,  PtAs2. 


Sulphate. 

1.   Kalinite,  Alum,  KA1(S04)2.12H20. 

ISOMETRIC  SYSTEM:  TETRAHEDRAL  CLASS. 
Sulphides,  etc. 


1.  Sphalerite,  ZnS. 

2.  Tiemannite,  HgSe. 


3.  Alabandite,  MnS. 


Sulphantimonites,  Sulpharsenites. 


1.  Tetrahedrite, 

Cu8Sb2S7  =  4Cu2S.Sb2S3. 


2.  Tennantite, 


Cu8As2S7=4Cu2S.As2S3. 


Borate. 

1.  Boracite,  Mg7Cl2B16030. 

TETRAGONAL   SYSTEM:   NORMAL  CLASS. 
Sulphide. 

1.   Stannite,  Cu2FeSnS4. 

Oxides  and  Closely  Related  Silicates  and  Phosphates. 


1.  Octahedrite,  Ti02. 

2.  Cassiterite,Sn02orSnSn04. 

3.  Rutile,  Ti02  or  TiTi04. 


4.  Zircon,  ZrSi04. 

5.  Thorite,  ThSi04. 

6.  Xenotime,  YP04. 


Carbonate. 

1.  Phosgenite,  (PbCl)2C03. 

Silicates. 


1.  Vesuvianite,  Complex 

Ca,Mg,Na,Al,Fe  silicate. 


2.   Apophyllite, 


H7KCa4(Si03)8.4iH,0 


LISTS  OF  MINERALS  357 

TETRAGONAL  SYSTEM:  TRI-PYRAMIDAL  CLASS. 

Silicate. 
1.  Wernerite  or  Scapolite,  CaiAUSiAj  with  NjuAla 

Tungstate  and  Molybdate. 

1.   Scheelite,  CaW04.  |   2.   Wulfenite,  PbMo04. 

TETRAGONAL  SYSTEM:  SPHENOIDAL  CLASS. 

Sulphide. 
1.  Chalcopyrite,  CuFeS2. 

HEXAGONAL  SYSTEM:   NORMAL  CLASS. 
Sulphides. 


1.   Molybdenite,  MoS2. 


3.   Pyrrhotite,  FenS, 


2.   Covellite,  CuS. 

Silicates. 


1.   Beryl,    Be3Al2(Si03)6    with 
some  [OH]?. 


2.  Nephelite,  NaAlSi04. 
(Approx.) 


HEXAGONAL  SYSTEM:  HEMIMORPHIC  CLASS. 
Sulphides,  etc. 

1.   Greenockite,  CdS.  |  2.   Niccolite,  NiAs. 

Oxide. 

1.   Zincite,  ZnO  with  MnO. 

HEXAGONAL   SYSTEM:  TRI-PYRAMIDAL  CLASS. 

Phosphates,  etc. 

Apatite  Group. 


1.  Apatite,  Ca4(CaF)(P04)3. 

2.  Pyromorphite, 

Pb4(PbCl)(P04)3. 


3.   Mimetite, 


Pb4(PbCl)(As04)3. 


4.   Vanadinite, 


Pb4(PbCl)(V04)3. 


358 


MANUAL  OF  MINERALOGY 


HEXAGONAL  SYSTEM:  RHOMBOHEDRAL  CLASS. 
NORMAL  DIVISION. 

Elements. 


4.  Bismuth,  Bi. 

5.  Tellurium,  Te. 


1.  Graphite,  C. 

2.  Arsenic,  As. 

3.  Antimony,  Sb. 

Sulphides,  Sulphantimonites,  Sulpharsenites. 


1.  Millerite,  NiS. 

2.  Pyrargyrite, 


3.  Proustite, 

AgsAsSs  or  3Ag2S.As2S3. 


Ag3SbS3  or  3Ag2S.Sb2S3. 

Oxides,  Hydroxides. 


1.  Corundum,  A1203. 

2.  Hematite,  Fe203. 


1.  Calcite,  CaC03. 

2.  Dolomite,  CaMg(C03)2 

(tri-rhombohedral) . 

3.  Magnesite,  MgC03. 


3.   Brucite,  Mg(OH)2. 


Carbonates. 
Calcite  Group. 

4.  Siderite,  FeC03. 

5.  Rhodochrosite,  MnC03. 

6.  Smithsonite,  ZnC03. 


1.  Tourmaline, 

R,Al,(B.OH)lSi401, 

(hemimorphic). 


Silicates. 

2.   Chabazite, 

(Ca,Na2)Al2Si4012.6H20?. 


Nitrate. 
1.  Soda-niter,  NaN03. 

HEXAGONAL  SYSTEM:  RHOMBOHEDRAL  CLASS. 
TRI-RHOMBOHEDRAL  DIVISION. 

Titanate. 

1.  Ilmenite,  FeTi03. 

Silicates. 

1.    Willemite,  Zn2Si04.  |  2.  Phenacite,  Be2Si04. 


LISTS  OF  MINERALS  359 

HEXAGONAL  SYSTEM:   RHOMBOHEDRAL  CLASS. 
TRAPEZOHEDRAL  DIVISION. 

Sulphide. 
1.  Cinnabar,  HgS. 

Oxide. 

1.   Quartz,  Si02. 

ORTHORHOMBIC   SYSTEM. 

Element. 
1.  Sulphur,  S. 


Sulphides,  etc. 


1.  Stibnite,  Sb2S3. 

2.  Bismuthinite,  Bi2S3. 

3.  Chalcocite,  Cu2S. 


4.  Stromeyerite,  CuAgS. 

5.  Marcasite,  FeS2. 

6.  Arsenopyxite,  FeAsS. 


Sulphantimonites,  etc. 


1.  Bournonite,  (Pb,Cu2)3Sb2S6 
or  3(Pb,Cu2)S.Sb2S3. 


2.  Stephanite,  Ag6SbS4  or 
5Ag2S.Sb2S3. 


Sulpharsenate. 

1.  Enargite,  CuaAsS4  or  3Cu2S.As2S6. 

Chlorides. 

1.  Atacamite,  Cu2Cl(OH)3.         |  2.   Carnallite,  KMgCL.6HA 

Oxides,  Hydroxides. 


1.  Chrysoberyl,  BeAl204. 

2.  Brookite,  Ti02. 

3.  Diaspore,  A1202(OH)2. 

4.  Goethite,  Fe202(OH)2. 


5.  Manganite,  Mn202(OH)2. 

6.  Pyrolusite,      Mn02     with 

about2%H20.    (Pseudo- 


morphous.) 


Carbonates. 
Aragonite  Group. 


1.  Aragonite,  CaC03. 

2.  Strontianite,  SrC03. 


3.  Witherite,  BaCO,. 

4.  Cerussite,  PbCO,. 


360 


MANUAL  OF  MINERALOGY 


1.  Enstatite,  Bronzite, 

Hypersthene, 
MgSi03,(Mg,Fe)Si03. 

2.  Anthophyllite,(Mg,Fe)Si03. 

3.  lolite, 


Silicates. 

9.  Prehnite,  H2Ca2Al2(Si04)3. 

10.  Calamine, 

H2(Zn20)Si04  (hemimor- 
phic). 

11.  Staurolite, 


(Mg,Fe)4Al6(A1.0H)2(Si207)5. 

4.  Chrysolite,  (Mg,Fe)2Si04. 

5.  Danburite,  CaB2(Si04)2. 

6.  Topaz,  (Al(F.OH))2Si04. 

7.  Andalusite,  (A10)AlSi04. 

8.  Zoisite, 

Ca(A1.0H)Al2(SiO4)3 


(Mg,Fe)(A1.0H)(A10)4(Si04)f. 

12.  Sillimanite,  Al2Si06. 

13.  Natrolite, 

Na2Al2Si3010.2H20. 

14.  Thomsonite 

(Na2,Ca)Al2(Si04)2.2|H20. 


Niobate,  Tantalate. 
1.  Columbite-tantalite,  (Fe,Mn)(Nb,Ta)206. 


Phosphates,  etc. 


1.  Triphylite-lithiophilite, 

Li(Fe,Mn)P04. 

2.  Olivenite,  Cu(Cu.OH)As04. 


3.  Scorodite,  FeAs04.2H20. 

4.  Wavellite, 

(A1.0H)3(P04)2.5H20. 


1.  Barite,  BaS04. 

2.  Celestite,  SrS04. 

3.  Anglesite,  PbS04. 


Nitrate. 
1.   Niter,  KN03. 

Sulphates. 

4.  Anhydrite,  CaS04. 

5.  Brochantite,  Cu4(OH)6S04. 


MONOCLINIC  SYSTEM. 
Sulphides,  Tellurides. 


1.  Realgar,  AsS. 

2.  Orpiment,  As2Sa. 


3.  Sylvanite,  AuAgTe4. 

4.  Calaverite,  AuTe». 


LISTS  OF  MINERALS 


361 


Sulphantimonite. 

1.  Polybasite,  Ag9SbS6. 

Fluoride. 
1.   Cryolite,  Na3AlF6. 

Hydroxide. 

1.   Gibbsite,  A1(OH)3. 


Carbonates. 


1.  Malachite,  (Cu.OH)2C03. 

2.  Azurite,Cu(Cu.OH)2(C03)2. 

3.  Aurichalcite, 
2(Zn,Cu)C03.3(Zn,Cu)  (OH)2. 


4.   Gay-Lussite, 


Na2C03.CaC03.5H20. 


Silicates. 


1.  Orthoclase,  KAlSi3Oa. 

2.  Pyroxene    Group,    R"Si03 

(R  =  Ca,Mg,Fe). 

3.  ^Egirite,  NaFe(Si03)2. 

4.  Jadeite,  NaAl(SiO3)2. 

5.  Spodumene,  LiAl(Si03)2. 

6.  Wollastonite,  CaSi03. 

7.  Pectolite,  HNaCa2(Si03)3. 


8.  Amphibole  Group, 

R"Si03(R  =  Ca,Mg,Fe). 

9.  Datolite,  Ca(B.OH)Si04. 

10.  Epidote, 

Ca2(A1.0H)Al2(SiC>4)3. 

11.  Allanite, 
Ca2(A1.0H)  (Al,Fe,Ce,La,Di), 

(Si04)3. 


1.  Heulandite, 

H4CaAl2(Si03)6.3H20. 

2.  Harmotome, 

(K2,Ba)Al2Si50]4.5H20. 

3.  Stilbite, 

(Na2,Ca)Al2Si6016.6H20. 


Hydrated  SiUcates. 

4.  Laumontite, 

H4CaAl2Si4014.2H20. 

5.  Scolecite, 

CaAl2Si30,0.3H20. 


362  MANUAL  OF  MINERALOGY 


Foliated,  Micaceous  Silicates. 


1.  Muscovite,  H2KAl3(Si04)3. 

2.  Lepidolite, 
KU(A1.2(OH,F))Al(SiOa)i. 

3.  Biotite, 

(H,K)2(Mg,Fe)2Al2(Si04)3.' 

4.  Phlogopite, 


6.  Margarite,  H2CaAl4Si20]2. 

7.  Clinochlore,  Chlorite, 

H8Mg5Al2Si3018. 

8.  Serpentine,  H4Mg3Si209. 

9.  Kaolin,  H4Al2Si209. 
10.  Talc,  H2Mg3(Si03)4. 


H2KMg3Al(Si04)3?.  I  11.  Pyrophyllite,  H2Al2(Si03)4. 

5.  Lepidomelane, 

(H,K)2Fe3(Fe,Al)4(Si04)5?. 

Titanosilicate. 
1.    Titanite,  CaTiSi08. 


Phosphates. 


1.  Monazite,  (Ce,La,Di)P04 

with  ThSi04. 

2.  Lazulite, 

Mg(A1.0H)2(P04)2. 


3.  Vivianite, 


Fe3(P04)2.8H20. 


Borates. 


1.  Colemanite, 


Ca2B6On.5H20. 


2.   Borax,  Na2B407.10H20. 


Sulphates,  Chromates. 


1.  Glauberite,  Na2Ca[S04]2. 

2.  Crocoite,  PbCr04. 


3.   Gypsum,  CaS04.2H20. 


Tungstates. 
1.  Wolframite,  FeW04.  |  2.  Hubnerite,  MnW04. 


LISTS  OF  MINERALS 


363 


TRICLINIC  SYSTEM. 
Silicates. 


1.  Microcline,  KAlSi308. 

Plagioclase  Feldspars. 

2.  Albite,  NaAlSi308. 

3.  Oligoclase,  3  Albite,  1  An- 

orthite. 

4.  Andesine,  1  Albite,  1  An- 

orthite. 


5.  Labradorite,  1  Albite,  3  An- 

orthite. 

6.  Anorthite,  CaAl2Si208. 

7.  Rhodonite,  MnSi03. 

8.  Cyanite,  Al2Si05. 

9.  Axinite,  Ca7Al4B2(Si04)8. 


Phosphate. 
1.  Amblygonite,  Li(AlF)P04. 

Sulphate. 
1.   Chalcanthite,  CuS04.5H20. 


AMORPHOUS  OR  MASSIVE  MINERALS. 
Oxides,  Hydroxides. 


1.  Opal,  Si02,  generally  with  3 

to  9%  H20. 

2.  Turgite,  Fe4O5(OH)2. 

3.  Limonite,  Fe403(OH)6. 


4.  Bauxite,  A120(OH)4. 

5.  Psilomelane,     Mn02     with 

MnO,  BaO,  CoO,  H20, 
etc. 


Silicates. 


1.  Genthite,    Garnierite, 
Ni,Mg,  silicates. 


2.  Chrysocolla,    CuSi03.2H20. 


Phosphate. 
1.  Turquois,   H(A1.20H)2P04  with  H(Cu.OH)2P04. 


V.  DETERMINATIVE  MINERALOGY. 

INTRODUCTION. 

Determinative  Tables  for  minerals  are  of  two  kinds:  (1)  those 
which  rely  chiefly  upon  chemical  tests,  and  (2)  those  which  make 
use  solely  of  physical  tests.  Obviously,  since  the  chemical  com- 
position of  a  mineral  is  its  most  fundamental  property,  those 
tables  which  emphasize  chemical  tests  are  much  the  more  satis- 
factory. On  the  other  hand,  the  tables  which  depend  wholly 
upon  physical  tests  have  distinct  limitations  beyond  which  it  is 
impossible  to  use  them.  These  latter  tables  have,  however,  the 
important  advantages  that  their  tests  are  simpler,  more  readily 
and  quickly  performed,  and  do  not  require  the  equipment  of  a 
laboratory.  For  these  reasons  physical  determinative  tables 
probably  have  a  wider  use,  in  spite  of  their  limitations,  than  those 
that  involve  chemical  tests. 

The  character  and  purpose  of  this  book  forbid  the  inclusion  of 
elaborate  chemical  tables  and  require  instead  the  introduction 
of  physical  tables  of  as  simple  a  form  as  possible.  Such  tables 
must,  however,  be  used  with  a  thorough  understanding  of  their 
nature  and  their  inherent  disadvantages.  Many  of  the  physical 
properties  of  minerals  are  not  entirely  fixed  in  their  character. 
Color,  for  instance,  is  frequently  an  extremely  variable  property. 
Hardness,  while  more  definite,  may  vary  to  a  slight  extent,  and 
by  a  change  in  the  structure  of  a  mineral  may  appear  to  vary 
much  more  widely.  Cleavage  is  a  property  which  may  often 
be  obscured  by  the  physical  condition  of  the  mineral.  Conse- 
quently in  making  a  determination  of  a  mineral  by  means  of  its 
physical  properties  alone,  it  is  necessary  to  have  a  fairly  typical 
specimen  and  one  which  is  of  sufficient  size  to  enable  its  charac- 
ters to  be  definitely  seen.  Often,  moreover,  it  will  be  impossible 
by  the  aid  of  such  tables  to  positively  differentiate  between  two 

364 


DETERMINATIVE  MINERALOGY  365 

or  three  similar  species.  Frequently,  however,  in  such  cases  the 
descriptions  of  these  possible  minerals  given  in  Section  IV  will 
enable  one  to  make  a  definite  decision.  Moreover,  the  tables 
that  follow,  used  in  connection  with  the  chemical  tests  given 
under  the  description  of  minerals  in  Section  IV,  together  with 
the  more  detailed  explanations  of  the  various  tests  to  be  found  in 
Section  III,  may  serve  as  a  substitute  for  more  elaborate  chemical 
tables. 

The  Determinative  Tables  given  beyond  have  been  made  as 
brief  and  simple  as  possible.  Only  the  common  species  or  those 
which,  while  rarer  in  occurrence,  are  of  economic  importance 
have  been  included.  The  chances  of  having  a  mineral  to  deter- 
mine that  is  not  included  in  these  tables  are  small,  but  it  must 
be  borne  in  mind  that  there  is  such  a  possibility.  The  names 
of  the  minerals  have  been  printed  in  three  different  styles  of  . 
type,  as  (see  page  373)  CHALCOCITE,  ARGENTITE  and  stephanite,  in 
order  to  indicate  their  relative  importance  and  frequency  of 
occurrence.  Whenever  it  was  felt  that  difficulty  might  be  ex- 
perienced in  correctly  placing  a  mineral,  it  has  been  included  in 
the  two  or  more  possible  divisions.  Usually,  however,  for  the 
sake  of  brevity,  the  detailed  description  of  such  a  mineral  has 
been  printed  in  full  only  upon  one  page. 

On  page  369  will  be  found  a  General  Classification  of  the 
tables.  The  proper  division  in  which  to  look  for  a  mineral  is  to 
be  determined  by  means  of  the  tests  indicated  there.  The  tables 
are  divided  into  two  main  sections  depending  upon  the  luster  of 
the  minerals  in  them.  The  first  division  includes  those  minerals 
which  have  a  Metallic  or  Submetallic  Luster.  By  that  is  meant 
those  minerals  which  on  their  thinnest  edges  remain  opaque 
and  which  consequently  will  give  black  or  dark-colored  " streaks" 
when  they  are  rubbed  across  a  piece  of  unglazed  porcelain,  the 
so-called  streak  plate.  Nonmetallic  minerals  are  those  which 
are  transparent  upon  their  thinnest  edges,  and  which  therefore 
give  either  a  colorless  or  a  light-colored  streak.  It  is  to  be 
noted  that  the  color  of  the  streak  cannot  always  be  foretold 
from  the  color  of  the  mineral  itself.  Frequently  a  dark-colored 
mineral  will  be  found  to  give  a  light-colored  streak. 


366  MANUAL  OF  MINERALOGY 

The  tables  are  next  subdivided  according  to  hardness.  The 
tests  used  in  the  General  Classification  are:  (1)  minerals  that  are 
soft  enough  to  leave  a  mark  when  rubbed  across  a  piece  of  paper; 
(2)  minerals  that  can  be  scratched  by  the  finger  nail;  (3)  those 
that  can  be  cut  by  a  cent;  (4)  minerals  that  are  softer  than  the 
steel  of  the  blade  of  an  ordinary  pocket  knife;  (5)  and  (6)  min- 
erals that  are  harder  than  a  knife  but  can  or  cannot  be  scratched 
by  quartz.  In  applying  the  tests  for  hardness,  certain  precau- 
tions should  be  observed.  Before  deciding  upon  the  relative 
hardness  of  a  mineral,  it  is  well  to  try  the  test  if  possible  in  two 
ways.  For  instance,  if  a  mineral  is  apparently  scratched  by  the 
edge  of  a  cent  make  sure  on  the  other  hand  that  the  cent  cannot 
be  scratched  by  the  mineral.  Further,  the  cent  and  the  knife 
blade  used  in  making  the  tests  should  be  bright  and  clean,  other- 
wise the  rubbing  off  of  a  layer  of  dirt  or  tarnish  might  be  mis- 
taken for  a  scratch.  In  the  tables  themselves,  the  hardness 
of  the  minerals  is  given  in  terms  of  the  Scale  of  Hardness,  see 
page  61.  The  possession  of  specimens  of  the  minerals  of  this 
scale,  so  that  the  hardness  of  a  mineral  could  be  closely  deter- 
mined, would  frequently  be  of  great  assistance  in  the  use  of  the 
tables.  Lastly,  it  is  to  be  remembered  that  the  physical  con- 
dition of  a  mineral  may  apparently  change  its  hardness.  For 
instance,  minerals  that  occur  at  times  in  pulverulent  or  fibrous 
forms  will  under  these  conditions  appear  to  be  much  softer  than 
when  in  their  more  usual  form.  Also  the  chemical  alteration 
of  a  mineral  will  commonly  change  its  hardness. 

The  minerals  with  nonmetallic  luster  are,  in  general,  further 
subdivided  according  to  whether  they  show  a  prominent  cleavage 
or  not.  This-will  frequently  be  a  difficult  decision  to  make.  It 
will  require  some  practice  and  experience  before  one  can  always 
make  the  determination  rapidly  and  accurately.  Note  that  the 
minerals  are  divided  according  to  whether  they  show  a  prominent 
cleavage  or  not.  Minerals  in  which  the  cleavage  is  imperfect 
or  ordinarily  obscure  are  included  with  those  that  have  no  cleav- 
age. It  will  always  be  best,  if  it  is  possible,  to  actually  try  to 
produce  a  cleavage  upon  the  specimen  rather  than  to  judge  from 
its  appearance  alone.  If  a  mineral  shows  a  cleavage,  the  num- 


DETERMINATIVE  MINERALOGY  367 

her  of  the  cleavage  planes,  their  relations  to  each  other  and  to 
any  crystal  forms  present,  etc.,  are  to  be  noted.  As  far  as  pos- 
sible, the  minerals  in  which  the  cleavage  may  become  obscure, 
because  of  certain  conditions  of  structure,  have  been  included 
in  both  divisions. 

The  minerals  which  fall  in  any  one  of  the  different  divisions 
of  the  tables  have  been  arranged  according  to  various  methods. 
In  some  cases,  those  that  possess  similar  cleavages  have  been 
grouped  together;  frequently  color  determines  their  order,  etc. 
The  column  farthest  to  the  left  will  indicate  the  method  of 
arrangement  used  in  each  section.  Most  of  the  different  prop- 
erties listed  and  the  more  general  facts  included  under  the 
headings,  Crystallization  and  Structure  and  Remarks,  need  no 
especial  explanation.  A  few  words,  however,  may  be  said  con- 
cerning the  column  headed  Specific  Gravity.  For  a  discussion 
of  specific  gravity  and  the  methods  for  its  accurate  determina- 
tion, see  page  62.  If  the  specimen  to  be  determined  is  of  suffi- 
cient size  and  is  pure,  its  approximate  specific  gravity  can  be 
determined  by  simply  weighing  it  in  the  hand.  In  order  to  do 
this,  however,  will  require  some  experience.  Below  is  given  a 
list  of  common  minerals  which  show  a  wide  range  of  specific 
gravity.  By  experimenting  with  specimens  of  these,  one  can 
become  quite  expert  in  the  approximate  determination  of  the 
specific  gravity  of  any  mineral. 

Halite,  2.14  Limonite,  3.80  Cerussite,  6.51 

Gypsum,  2.32  Corundum,  4.03  Cassiterite,  6.95 

Orthoclase,  2.56  Chalcopyrite,  4.20  Galena,  7.50 

Calcite,  2.72  Barite,  4.48  Cinnabar,  8.10 

Fluorite,  3.18  Pyrite,  5.03  Copper,  8.84 

Topaz,  3.53  Chalcocite,  5.75  Silver,  10.60 

When  the  subdivisions  of  the  tables  are  studied,  the  following 
interesting  and  important  facts  are  to  be  noted.  The  majority 
of  the  minerals  with  metallic  luster  are  sulphides.  Most  of  them 
are  softer  than  a  knife.  The  only  sulphides  that  are  harder.than 
a  knife  are  Pyrite,  Marcasite  and  Arsenopyrite.  The  greater 
part  of  minerals  with  metallic  or  submetallic  luster  that  are 


368  MANUAL  OF  MINERALOGY 

harder  than  a  knife  are  oxygen  compounds  of  iron.  Among  the 
minerals  with  nonmetallic  luster,  it  is  to  be  noted  that  those 
which  are  harder  than  a  knife  are,  with  very  few  exceptions, 
either  silicates  or  oxides.  Comparatively  few  silicates  are  to  be 
found  among  the  minerals  of  nonmetallic  luster  which  are  softer 
than  a  knife.  It  is  to  be  further  noted  that  the  majority  of  such 
silicates  contain  water  in  some  form.  On  the  other  hand, 
the  greater  part  of  the  carbonates,  sulphates,  phosphates,  etc., 
are  to  be  found  in  these  sections. 


GENERAL  CLASSIFICATION  OF  THE 
TABLES. 

A.  METALLIC  OR  SUBMETALLIC  LUSTER. 
I.  Very  Soft.     Will  Readily  Leave  a  Mark  on  Paper, 

p.  370. 
II.   Can  be  Scratched  by  a  Knife,  but  Will  not  Readily 

Leave  a  Mark  on  Paper,  p.  372. 
III.   Cannot  be  Scratched  by  a  Knife,  p.  382. 

B.  NONMETALLIC   LUSTER. 

I.   Minerals  which  Give  a  Definitely  Colored  Streak, 

p.  386. 
U.   Minerals  which  Give  a  Colorless  Streak. 

1.  Can  be  scratched  by  the  finger  nail,  p.  392. 

2.  Cannot  be  scratched  by  the  finger  nail,  but  can 

be  scratched  by  a  cent. 
a.   Show  a  prominent  cleavage,  p.  396. 
6.   Do  not  show  a  prominent  cleavage. 

1.  A  small  splinter  is  fusible  in  the 

candle  flame. 

a.  Readily  soluble  in  water;  yield  a 

taste,  p.  398. 

b.  Insoluble  in  water,  p.  400. 

2.  Infusible  in  the  candle  flame,  p.  400. 

3.  Cannot  be  scratched  by  a  cent,  but  can  be 

scratched  by  a  knife. 

a.  Show  a  prominent  cleavage,  p.  402. 

b.  Do  not  show  a  prominent  cleavage,  p.  410. 

4.  Cannot  be  scratched  by  a  knife,   but  can  be 

scratched  by  quartz. 
a.   Show  a  prominent  cleavage,  p.  414. 
6.   Do  not  show  a  prominent  cleavage,  p.  420. 

5.  Cannot  be  scratched  by  quartz. 

a.  Show  a  prominent  cleavage,  p.  426. 

b.  Do  not  show  a  prominent  cleavage,  p.  428. 

369 


METALLIC   OR 
I.     Very  soft.     Will  readily 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

Black. 

Iron-black. 

2-2.5.     Marks 
paper  easily. 

F.     Splintery. 

4.7 

Steel-gray  to 
iron-black. 

1-1.5.     Marks 
paper  easily. 

One  perfect  C. 

2.2 

Gray-black. 

Blue-black   or 
lead-gray. 

1-1.5.     Marks 
paper  easily. 

One  perfect  C. 

4.7 

2.    Marks  paper 
easily. 

One  perfect  C. 

4.5 

2.5.     Marks  paper 
with  difficulty. 

Perfect  cubic  C. 

7.6 

Bright  red. 

Red  to  vermil- 
ion. 

Marks  paper  with 
difficulty. 

8.1 

Red-brown. 

Red-brown. 

Vlarks  paper  eas- 

ly. 

5.2 

Yellow-brown 

Yellow- 
brown. 

Marks  paper  eas- 

ly. 

3.6-4.0 

See  also  covellite,  p.  377,  and  argentite,  p.  373, 


370 


SUBMETALLIC   LUSTER, 
leave  a  mark  on  paper. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Usually  radiating  fibrous  or 
splintery. 

Distinguished  from  other  minerals 
of  this  group  by  its  structure. 

PYROLUSITE. 

Mn02. 

Rhombohedral.    Micaceous. 

May  be  in  hexagonal-shaped  leaves. 
Told  irom  molybdenite  by  the 
brown  tinge  to  its  black  color. 
Greasy  feel. 

GRAPHITE. 
C. 

Hexagonal.    Micaceous. 

May  be  in  hexagonal-shaped  leaves. 
Told  from  graphite  by  the  blue 
tinge  to  its  black  color  and  its 
higher  specific  gravity.  Greasy  feel. 

Molybdenite. 
MoS2. 

Orthorhombic.       B  1  a  d  e  d 
structure  or  in  slender  radi- 
ating crystals. 

Characterized  by  its  long  and 
bright  cleavage  faces.  Fuses  in  the 
candle  flame. 

STIBNITE. 

Sb2S3. 

In  cubic  crystals  or  cleavage 

masses. 

See  p.  375. 

GALENA. 
PbS. 

Earthy. 

The  earthy  form  of  cinnabar  is  not 
common. 

CINNABAR. 

HgS. 

Earthy. 

The  earthy  form  of  hematite  is 
often  known  as  red  ochre  or  paint 
ore. 

HEMATITE. 
Fe203. 

Earthy. 

The  earthy  form  of  limonite  is 
often  known  as  yellow  ochre. 

LIMONITE. 

Fe4O3(OH)8. 

which  may  leave  a  slight  mark  on  paper. 


371 


METALLIC   OR 
II.     Can  be  scratched  by  a  knife, 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

Soft  black. 

Iron-black. 

2-2.5.     Very  soft. 
Will  mark  paper. 

F.    Splintery. 

4.7 

Black,  with 
sometimes  a 
brown  tinge. 

Iron-black. 

5-6.     U.  harder 
than  knife. 

F.     Irregular. 

4.3 

Gray-black. 

Steel-gray  on  fresh 
surface,  tarnishing 
to  dead  black  on 
exposura. 

2.5-3. 

F.    Irregular. 

5.7 

Black,  with 
sometimes  a 
brown  tinge. 

Steel-gray,  some- 
times tarnishes  to 
dead  black  on  ex- 
posure. 

3-4. 

F.    Irregular. 

4.7-5.0 

Black. 

Gray-black. 

3. 

C.     Perfect  prismatic. 
F.    Uneven. 

4.4 

2-2.5. 

F.    Uneven. 

7.3 

2-2.5. 

F.    Uneven. 

6.2 

2-3. 

F.    Uneven. 

6-6.2 

2.5-3. 

F.    Uneven. 

6.2-6  3 

2-3. 

F.    Fibrous 

5.5-6 

372 


SUBMETALLIC   LUSTER. 

but  will  not  readily  leave  a  mark  on  paper. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Usually  radiating  fibrous  or 
splintery. 

Usually  to  be  told  by  its  struc- 
ture and  soft  black  streak. 

PYROLUSITE. 

Mn02. 

See  p.  385. 

Psilomelane. 
MnO2  with  MnO,  etc. 

Orthorhombie.     Compact 
massive. 

Often  associated  with  other  cop- 
per ores,  such  as  bornite,  chalco- 
pyrite,  malachite,  etc. 

CHALCOCITE 

(Copper  Glance). 

Isometric,  tetrahedral. 
Massive    or    in    tetrahedral 
crystals. 

Often  associated  with  chalcopy- 
rite,  pyrite,  silver  ores,  etc. 

TETRAHEDRITE 

(Gray  Copper). 
4Cu2S.Sb2S3. 

Orthorhombie.  In  bladed 
masses,  showing  long  cleav- 
age faces.  More  rarely  in 
stout  prismatic  crystals. 

A    rare    mineral,    found    usually 
with  other  copper  minerals. 

Enargite. 
SCuzS.ASjSs. 

Isometric.  Usually  irregu- 
lar massive  or  earthy.  At 
times  in  small  isometric 
crystals,  commonly  cubes. 

Distinguished    by    being   easily 
sectile,  i.e.,  it  can  be  cut  with  a 
knife,    like   lead.     Bright   steel- 
;ray  on  fresh  surface  but  tarnish- 
ing to  a  dull  gray-black  on  expos- 
ure. 

Argentite. 
Ag2S. 

Orthorhombie.  In  small  ir- 
regular masses,  often  earthy. 
At  times  in  stout  six-sided 
prismatic  crystals. 

®     A    rare    mineral.    Bright 
G     steel-gray  on  a  fresh  sur- 
tg     face   but   tarnishing   to   a 
c     dull  gray-black  on  expos- 

1  ure' 

Stephanite. 
5Ag2S.Sb2S,. 

Monoclinic.  Often  in  thin 
six-aided  crystal  plates  with 
triangular  markings  on  top. 
Also  massive  and  earthy. 

•£     A  rare  mineral. 

a 
>> 

1 

Polybasite. 
9(Ag,Cu)2S.Sb,S,. 

Irregular  massive. 

|     A    rare    mineral.    To    be 
positively    told    only    by 
~     chemical  tests. 

Stromeyrite. 
CuAgS. 

In  fibrous,  feather-like 
masses. 

cr 
$     Characterized  usually  by 
J|     its  fibrous  structure. 

Jamesonite 
(Feather  ore). 
2PbS.Sb2S,. 

1 

373 


METALLIC   OR 
II.     Can  be  scratched  by  a  knife,  but  will 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

Black. 

Gray-black. 

2.5-3. 

F.    Uneven. 

5.8 

4. 

F.     Uneven. 

4.4 

Gray-black. 

Blue-black  or 
lead-gray. 

Will  leave  a  mark 
on  paper. 

One  perfect  cleavage. 

4.5 

6.4 

2.5.     Marks  paper 
with  difficulty. 

Perfect  cubic  cleavage. 

7.6 

Tin-white,  tar- 
nishing to  dark 
gray. 

3.5. 

One  good  cleavage  but 
seldom  seen. 

5.7 

Tin-vvhite. 

3-3.5. 

One  good  cleavage  seen 
in   the   more   coarsely 
crystallized  type. 

6.6 

2-2.5. 

Perfect  prismatic 
cleavage    in    3    direc- 
tions. 

6.1-6.3 

374 


SUBMETALLIC  LUSTER. 

not  readily  leave  a  mark  on  paper.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Orthorhombic.  In  stout  six- 
sided  prismatic  crystals. 
Often  twinned  with  reen- 
trant angles,  giving  a  "  cog- 
wheel "  effect.  Also  mas- 
sive granular. 

Commonly'called  "  cog-wheel  ore" 
because  of  the  characteristic  group- 
ing of  its  crystals.  Easily  fusible 
in  the  candle  flame.  Not  to  be 
positively  identified  when  massive 
except  by  chemical  tests. 

Bournonite. 
2PbS.Cu2S.Sb,S,. 

Tetragonal.  Irregular  mas- 
sive. 

Decrepitates  violently  in  the  can- 
dle flame.  Sometimes  shows  a 
bluish  tarnish. 

Stannite 
(Tin  Pyrites). 
Cu2S.FeS.SnS2. 

Orthorhombic.  Bladed 
structure  or  in  slender  radi- 
ating crystals. 

Characterized  by  its  long  bright 
cleavage  faces.  Fuses  easily  in  the 
candle  flame. 

STIBNITE. 

Sb2S3. 

Orthorhombic.  In  long 
slender  crystals,  often  radi- 
ating. Frequently  bladed. 

Fuses  in  candle  flame.  A  rare 
mineral.  To  be  positively  told 
from  stibnite  only  by  a  test  for  bis- 
muth. 

Bismuthinite. 
Bi2S3. 

Isometric.  Crystallized  or 
(cleavable)  granular. 

If  a  small  fragment  is  held  in  a 
candle  flame  it  does  not  fuse  but  is 
slowly  reduced  and  small  globules 
of  metallic  lead  collect  upon  the 
surfaces. 

GALENA. 

PbS. 

Rhombohedral.  Usually 
fine  granular,  often  with  bot- 
ryoidal  structure. 

Tarnishes  more  readily  than  the 
other  similar  minerals.  Heated  in 
the  candle  flame  does  not  fuse  but 
gives  off  a  white  smoke  and  yields 
a  strong  garlic  odor.  A  rare  min- 
eral. 

Arsenic. 

As. 

Rhombohedral.  Usually 
fine  granular. 

Usually  bright  in  luster.  Heated 
in  candle  flame  does  not  fuse  read- 
ily, gives  off  a  white  smoke  but  no 
odor.  A  rare  mineral. 

Antimony. 
Sb. 

Rhombohedral.  In  cleav- 
able masses. 

Characterized  by  bright  luster  and 
prominent  cleavage.  Heated  in 
candle  flame  fuses  very  easily.  A 
rare  mineral,  often  associated  with 
the  gold  and  silver  tellurides.  See 
under  sylvanite,  below. 

Tellurium. 
Te. 

375 


METALLIC   OR 
II.   Can  be  scratched  by  a  knife,  but  will 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

Gray-black. 

Tin-white. 

1.5-2. 

One  perfect  C. 

8-8.7 

2.5. 

F.    Uneven. 

9.3 

Black. 

Usually  pale  cop- 
per-red. See  p.  382. 

5-5.5. 

F.     Uneven. 

7.5 

Brownish  bronze 
but  when  exposed 
to  the  air  rapidly 
takes  on  a  purple 
tarnish. 

3. 

F.     Uneven. 

4.9-5  4 

Brownish  bronze. 

4. 

F.     Uneven. 

4.6 

3.5-4. 

C.    Octahedral. 

4.9 

Brass-yellow. 

3.5. 

F.    Uneven. 

4.2 

Brass-yellow,  al- 
most greenish 
when  in  very 
slender  crystals. 

3-3.5. 

F.    Uneven. 
C.    Rhombohedral 
but  seldom  seen. 

5.6 

Indigo-blue,  may 
tarnish  to  blue- 
black. 

1.5-2. 

Perfect  basal  C. 

4.6 

See  also  wolframite,  p.  379,  which  may  give  nearly  a  black  streak. 

376 


SUBMETALLIC  LUSTER. 

not  readily  leave  a  mark  on  paper.     (Continued.) 


Crystallization  and. 
Structure. 

Remarks. 

Name  and 
Composition. 

Monoclinic.  In  thin  lath- 
shaped  crystals.  Often  as 
thin  coatings  on  surfaces  of 
rock  arranged  like  ancient 
forms  of  writing. 

Fuses  very  easily  in  candle  flame. 
A  rare  mineral.  Often  to  be  posi- 
tively told  from  tellurium  and  the 
other  similar  tellurides  only  by 
chemical  tests  (see  p.  157)  . 

Sylvanite. 
AuAgTe4. 

Monoclinic.  In  irregular 
small  masses  or  in  thin, 
deeply  striated  lath-shaped 
crystals. 

Easily  fusible  in  candle  flarr.e. 
Takes  on  at  times  a  faint  yellow 
color.  A  very  rare  mineral.  Told 
from  tellurium  and  sylvanite  by  its 
lack  of  cleavage,  but  for  positive 
identification  may  need  chemical 
tests. 

Calaverite. 
AuTe2. 

Hexagonal,  hemimorphic. 
Massive. 

See  p.  383. 

Niccolite. 
NiAs. 

Isometric.  Massive. 

Recognized  usually  by  its  promi- 
nent purple  tarnish.  Associated 
with  other  copper  ores,  chiefly 
chalcocite  and  chalcopyrite. 

BORNITE. 

Cu5FeS4. 

Hexagonal.  Massive. 

Recognized  usually  by  its  charac- 
teristic color.  Small  fragments 
often  magnetic.  Often  associated 
with  chalcopyrite  and  pyrite. 
Frequently  carries  nickel. 

PYRRHOTITE. 
Feats*. 

Isometric.'  Granular. 

A  rare  mineral  resembling  closely 
pyrrhotite,  with  which  it  is  inti- 
mately associated.  Distinguished 
from  pyrrhotite  by  its  cleavage. 

Pentlandite. 

(Ni.Fe)S. 

Tetragonal,  sphenoidal.  Us- 
ually massive.  Sometimes 
in  small  tetrahedral-shaped 
crystals. 

Usually  recognized  by  its  color  and 
softness.  Associated  with  pyrite, 
chalcocite,  bornite,  etc. 

CHALCOPYRITE 

(Copper  Pyrites). 

Rhombohedral.  In  radiat- 
ing groups  of  hair  like  crys- 
tals. 

Commonly  called  capillary  pyrites 

Millerite. 

NiS. 

Hexagonal.  In  platy  masses 
or  in  thin  six-sided  platy 
crystals. 

A  rare  mineral.  Characterized 
chiefly  by  its  color.  Tarnishes 
to  blue-black  on  exposure.  Mois- 
tened with  a  drop  of  water  turns 
purple. 

Covellite. 
CuS. 

377 


METALLIC   OR 
II.     Can  be  scratched  by  a  knife,  but  will 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

Steel-gray  to  iron- 
black. 

4. 

One  good  C. 
F.     Splintery. 

4.3 

Dark-brown 
to  black. 

F.     Uneven. 

4.3 

Iron-black  to 
brownish  black. 

5.5.    Scratched  by 
knife  with  diffi- 

culty if  at  all. 

One  good  C. 

7.2-7.5 

F.    Uneven. 

See  also  psilomelane  and  tetrahedrite,  p.  373,  which  may  give  brown-black  streaks. 


Light  to  dark 
brown. 

Dark  brown  to 
coal-black. 

3.5-4. 

Perfect  C.  in  six  direc- 
tions (dodecahedral). 

4.1 

Red-brown. 
Indian-red. 

Dark  brown  to 
steel-gray  to 
black. 

5.5-6.5.     Softer  in 
some  earthy  vari- 
eties but  usually 
harder  than  a 
knife. 

F.    Uneven  or  fibrous. 

5.2 

F.    Splintery. 

4.1 

Deep  red  to  black. 

2.5. 

C.     Rhombohedral. 
F.    Conchoidal. 

5.8 

Red-brown  to 
deep  red.      Ruby- 
red  in  transparent 
variety. 

3.5-4. 

F.    Uneven. 

6.0 

378 


SUBMETALLIC   LUSTER. 

not  readily  leave  a  mark  on  paper.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Orthorhombic.  In  radiating 
fibrous  or  crystalline  masses. 
Sometimes  in  distinct  pris- 
matic crystals,  often  grouped 
in  bundles. 

Often  closely  resembles  pyrolusite, 
with  which  it  is  frequently  associ- 
ated, but  is  to  be  distinguished 
rom  the  latter  by  its  greater  hard- 
ness and  dark-brown  streak. 

MANGANITE. 
MnO(OH)  = 
MnAi.HjO. 

Usually  in  granular  masses. 

See  p.  385. 

CHROMITE 
[Chromic  Iron). 

FeO.CrjOs. 

Monoclinic.  In  bladed 
masses.  Granular  to  mas- 
sive. 

Characterized  by  bladed  structure 
showing  good  cleavage  parallel  to 
ength  of  crvstal.  As  the  amount 
of  manganese  contained  in  the  min- 
eral increases  it  becomes  browner 
in  color  and  streak  and  graduates 
toward  hubnerite,  MnWO4. 

Wolframite. 
(Fe.  Mn)WO4. 

Isometric,  tetrahedral. 
Usually  cleavable  granular. 

VIost  sphalerite  is  nonmetallic  and 
strongly  resinousin  its  luster.  With 
increase  in  the  amount  of  iron  pres- 
jnt  it  becomes  dark  brown  to 
black.  The  darker  varieties  can 
often  be  told  by  scratching  a  cleav- 
age surface  with  a  knife  and  noting 
the  reddish  mark  left.  The  color 
of  the  streak  is  always  much 
lighter  than  the  color  of  the  speci- 
men. 

SPHALERITE 

(Zinc  Blende,  Black 
Jack,  etc.). 

(Zn.Fe)S. 

See  p.  385. 

HEMATITE. 
FezOa. 

See  p.  385. 

Turgite. 
Fe40<(OH)2= 
2FeA.H20. 

Rhombohedral.    Irregular 
massive. 

The  dark  Ruby  Silver,  showing 
dark  ruby  color  in  thin  splinters. 
See  p.  387. 

Pyrargyrite. 
3Ag2S.Sb2S3. 

Isometric.  Massive  or  rarely 
in  isometric  crystals,  cubes 
or  octahedrons.  Sometimes 
in  very  slender  crystals 
(chalcotrichite  or  plush  cop- 
per). 

Characterized  by  its  submetallic 
luster  and  red  streak.  Associated 
with  other  copper  minerals,  espe- 
cially malachite  and  native  copper. 

CUPRITE. 
Cu2O. 

379 


METALLIC   OR 
II.     Can  be  scratched  by  a  knife,  but  will 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

Yellow- 
brown.     Yel- 
low ocher. 

Dark  brown  to 
black. 

5-5.5.    Softer  in 
some  varieties  but 
usually  harder 
than  a  knife. 

F.     Splintery. 

3.6-4.0 

One  good  C. 
F.     Splintery. 

4.3 

Dark  red. 

Dark  red  to  ver- 
milion. 

2-2.5.    Some 
earthy  varieties 
are  soft  enough  to 
mark  paper. 

F.     Uneven. 
Prismatic  C.,  seldom 
seen. 

8.1 

Copper-red, 

shiny. 

Copper-red, 
black  tarnish. 

2.5-3. 

F.     Hackly. 

8.8 

Silver-white, 
shiny. 

Silver-white,  gray 
to  black  tarnish. 

2.5-3. 

F.     Hackly. 

10.5 

Gray,  shiny. 

Whitish,  or  steel- 
gray. 

4-4.5. 

F.     Hackly. 

14-19 

Silver-white, 
shiny. 

Silver-white  with 
a  reddish  tone. 

2-2.5. 

Perfect  basal  and 
rhombohedral  C. 

9.8 

Gold-yellow, 
shiny. 

Gold-yellow. 

2.5-3. 

F.     Hackly. 

19 

Olive-green. 

Iron-black  with  a 
brown  tarnish. 

3.5-4. 

C.    Cubical. 

3.9 

380 


SUBMETALLIC   LUSTER. 

not  readily  leave  a  mark  on  paper,     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

See  p.  387. 

LIMONITE 

(Bog  Iron  Ore). 
Fe403(OH)6= 
2Fe203.3H20. 

See  p.  387. 

Goethite. 
FeO(OH)  = 
Fe203.H2O. 

Rhombohedral.  Usually 
fine  granular  or  earthy. 

Usually  impure  and  of  a  dark-red  or 
brown  color.  When  pure  is  trans- 
lucent to  transparent  and  of  a  bright 
red  color.  Very  heavy. 

CINNABAR. 
HgS. 

Isometric.  Usually  in  irreg- 
ular grains.  May  be  in 
branching  crystal  groups  or 
in  rude  isometric  crystals. 

A  metal.  Malleable.  Very  heavy. 

COPPER. 
Cu. 

A  metal.  Malleable.  Very  heavy. 

SILVER. 
Ag. 

Isometric.  Irregular  grains 
or  nuggets. 

A  metal.  Malleable.  Very  heavy. 
Unusually  hard  for  a  metal.  Very 
rare. 

Platinum. 
Pt. 

Rhombohedral.  In  cleav- 
able  granular  masses. 

A  metal.  Sectile.  When  ham- 
mered out  is  at  first  malleable  but 
soon  breaks  up  into  small  pieces. 
Easily  fusible  in  the  candle  flame. 
A  rare  mineral. 

Bismuth. 
Bi. 

Isometric.  In  irregular 
grains,  nuggets,  leaves,  etc. 

A  metal.  Malleable.  Very  heavy. 

GOLD. 
Au. 

Isometric,  tetrahedral.  In 
granular  cleavable  masses. 

A  rare  mineral.  Characterized  by 
its  brown  tarnish,  olive-  green 
streak  and  cubical  cleavage. 

Alabandite. 
MnS. 

381 


METALLIC   OR 
III.     Cannot  be  scratched 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

6-6.2 

Black. 

Silver  or  tin  white. 

5.5-6. 

F.     Uneven. 

5.5-6. 

F.     Uneven. 

5.5-6 

p.5. 

F.     Uneven. 

5.5 

5.5. 

F.     Uneven. 

4.9 

Usually  pale  cop- 
per-red.   Some- 
times almost  sil- 
ver-white with 
pink  tone. 

5-5.5. 

F.     Uneven. 

7.5 

Pale  brass-yellow. 

6-6.5 

F.     Uneven. 

5.0. 

Pale  yellow  to  al- 
most white. 
Yellowish  tarnish. 

6-6.5 

F.     Uneven. 

4.9 

Black. 

6. 

F.    Uneven.    At  times 
shows  octahedral  part- 
ing. 

5.18 

382 


SUBMETALLIC   LUSTER, 
by  a  knife. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Orthorhombic.  Massive 
granular.  Sometimes  in 
crystals. 

Vhen  crystallized  is  commonly 
ound  in  diamond-shaped  tabular 
crystals  with  striations  running 
>arallel  to  the  shorter  diagonal  of 
he  diamond.  Sometimes  in  fan- 
shaped  twins. 

ARSENOPYRITE 

Mispickel). 
FeAsS. 

Isometric,  pyritohedral. 
Massive. 

Rare  minerals  found  with  other  co- 
)alt  and  nickel  species. 

Smaltite- 
Uhloanthite. 
CoAs2-NiAs2. 

Isometric,  pyritohedral. 
Usually  massive. 

Flare  minerals  found  with  other  co- 
salt  and  nickel  species.  Cobaltite 
shows  a  faint  reddish  tone  to  its 
silver  color. 

Cobaltite- 
Gersdorffite. 
CoAsS-NiAsS. 

Isometric.  In  fine  granular 
masses  or  in  small  octahe- 
dral crystals. 

A  rare  mineral. 

Linnseite. 

(Co,Ni)3S4. 

Hexagonal,  hemimorphic. 
Massive. 

Recognized  chiefly  by  its  color  and 
streak.  A  rare  mineral  found  with 
other  nickel  and  cobalt  ores. 

Niccolite. 
NiAs. 

Isometric,  pyritohedral 
Massive  granular.  Often  in 
striated  cubes,  octahedrons 
pyritohedrons,  etc. 

Most  common  sulphide.  Will 
strike  fire  with  steel. 

PYRITE 

(Iron  Pyrites). 
FeS2. 

Orthorhombic.  Often  in  ra- 
diating fibrous  masses.  In 
crystal  groups. 

Found  in  nodules  and  stalactites 
Not  nearly  so  common  as  pyrite 
Usually  distinguished  from  pyrite 
by  its  lighter  color  and  character- 
istic crystals,  but  it  may  require  a 
chemical  test  to  positively  differ- 
entiate them  (seep.  156). 

MARCASITE 
(White    Iron    Py- 
rites). 
FeSj. 

Isometric.  Usually  coarse  to 
fine  granular.  At  times  in 
crystals,  usually  octahe 
drons. 

Strongly  magnetic.  No  other  min 
eral  exhibits  this  property  as 
strongly. 

MAGNETITE. 
Fe30<. 

383 


METALLIC   OR 
III.     Cannot  be  scratched 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

Very  dark 
brown  to 
black. 

Black. 

5.5. 

F.    Uneven. 

9-9.7 

5.5-6 

F.    Uneven. 

4.3 

Black. 

5-6. 

F.    Uneven. 

4.3 

6. 

F.    Uneven. 

5.3-7.0 

Dark  brown. 

Iron-black  to 
brownish  black. 

5.5-6. 

One  good  C. 
F.    Uneven. 

7.2-7.5 

F.    Uneven. 

4.6 

F.     Uneven. 

5.1 

Red-brown. 
Indian-red. 

Dark  brown  to 
steel-gray  to 
black 

5.5-6.5. 
Softer  in  some 
earthy  varieties. 

F.    Uneven  or  fibrous. 

5.2 

F.    Splintery. 

4.1 

384 


SUBMETALLIC   LUSTER, 
by  a  knife.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Isometric.       Massive  eranu- 

Characterized  bv  its  black  color 

Uraninite 

Rarely  in  octahedral  crys- 
tals. 

mineral  in  which  the  rare  elements 
helium  and  radium  have  been 
found. 

^irncn  oienae;. 
Uncertain    composi- 
tion.   Chiefly  oxidea 
of  uranium. 

Rhombohedral.  In  grains  as 
sand;  massive  granular;  platy 
crystals. 

Sometimes  slightly  magnetic. 
Often  associated  with  magnetite. 

ILMENITE 
(Titanic  Iron). 
FeTi03  with  FejOs. 
Sometimes  much 
Mg. 

Compact  massive,  some- 
times stalactitic  or  botryoi- 
dal. 

Dull-black  luster.  Often  associ- 
ated with  other  manganese  ores 
rom  which  it  is  told  by  its  greater 
lardness. 

Psilomelane. 
Uncertain  composi- 
tion.  MnO2  with 
MnO,  H20,  BaO, 
K2O,  etc. 

Orthorhombic.  Granular  or 
in  stout  prismatic  crystals. 

Black  shiny  luster  on  fresh  surface. 
Sometimes  takes  on  a  slight  bluish 
tarnish. 

3olumbite- 
Tantalite. 
(Fe,Mn)Nb2Oe 
with  (Fe,Mn)Ta2O«. 

In  bladed  masses. 

See  p.  379. 

Wolframite. 
(Fe,Mn)WO4. 

Isometric.  Usually  in  granu- 
lar masses.  Rarely  in  small 
octahedral  crystals. 

Characterized  often  by  a  pitchy 
luster  and  accompanied  frequently 
by  traces  of  a  yellow  oxidation 
product. 

CHROMITE. 
(Chromic  Iron). 
FeCr204. 

Isometric.  Granular  or  in 
octahedral  crystals. 

Occurs  at  Franklin  Furnace,  N.  J., 
usually  in  intimate  association  with 
zincite  (red)  and  willemite  (green). 

FRANKLINITE. 
(Fe.Zn.Mn)O 
(Fe,Mn)2O8. 

Rhombohedral.  Radiating, 
reniform,  crystallized,  mica- 
ceous. 

Recognized  usually  by  its  red- 
brown  streak.  When  in  fibrous 
mammillary  forms  cannot  be  posi- 
tively told  from  the  rare  mineral 
turgite  except  by  proving  the  ab- 
sence of  water  in  its  composition  by 
heating  in  a  closed  tube. 

HEMATITE. 

FejOs. 

Radiating  reniform  and  sta- 
lactitic. 

A  rare  mineral  usually  associated 
with  limonite.  For  positive  iden- 
tification see  above. 

Turgite 
(Hydro-hematite). 
Fe4O6(OH)2= 
2Fe2O3.H2O. 

385 


METALLIC   OR 
III.     Cannot  be  scratched 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

F.    Splintery. 

3.6-4.0 

Va11<->_ 

brown. 

black. 

Softer  in  some 
earthy  varieties. 

One  good  C. 
F.    Splintery. 

4.3 

NONMETALLIC 
I.     Give  a  definitely 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

Dark  red. 

Dark  red  to  ver- 
million. 

2-2.5. 

F.    Uneven. 

8.1 

Red-brown. 
Ruby-red  when 
transparent. 

3.5-4. 

F.    Uneven. 

6.0 

Red-brown. 
Indian-red. 

Dark  brown  to 
steel-gray,  to 
black. 

5.5-6.5. 

F.    Splintery. 

5.2 

4.1 

Deep  red  to  black. 

2.5. 

F.    Conchoidal. 

5.8 

Bright  red. 

Ruby-red. 

2-2.5. 

F.    Conchoidal. 

5.5 

386 


SUBMETALLIC   LUSTER. 

by  a  knife.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Radiating  fibrous  in  mam- 
millary  or  stalactitic  forms. 

Characterized  by  its  streak  and 
structure.  Not  always  to  be  posi- 
tively told  from  the  rarer  mineral 
goethite,  except  by  an  estimation  of 
the  water  present.  Limonite  con- 
tains 15%,  goethite  10%  of  water. 

LIMONITE 

(Bog  Iron  Ore). 
Fe4O3(OH)8= 
2Fe2O3.3H2O. 

Orthorhombic.        Radiating 
fibrous    in    mammillary    or 
stalactitic   forms.       Some- 
times  in   groups   of   slender 
radiating   crystals.       More 
rarely  in  distinct  prismatic 
crystals. 

Told  definitely  from  limonite  if  it 
shows  cleavage  or  any  crystal  struc- 
ture. Otherwise  to  be  distin- 
guished only  as  described  above. 

Goethite. 
FeO(OH)  = 
Fe203.H20. 

LUSTER, 
colored  streak. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Rhombohedral.    Usually 
fine  granular  or  earthy. 

See  p.  381. 

CINNABAR. 

HgS. 

Usually  massive. 

See  p.  379. 

CUPRITE 
(Ruby  Copper). 
Cu20. 

Reniform,  crystalline,  mica- 
ceous, earthy. 

See  p.  385. 

HEMATITE. 

Fe203. 

Reniform  and  stalactitic. 

See  p.  385. 

Turgite. 
Fe4O8(OH)2= 
2Fe203.H20. 

Rhombohedral.  Irregular 
massive.    Rarely  in  crystals. 

The  dark  "  ruby  silver  "  showing 
dark  ruby-red  color  in  thin  splin- 
ters. A  rare  mineral  associated 
with  proustite,  stephanite,  polybas- 
site,  argentite,  etc.  Easily  fusible 
in  the  candle  flame. 

Pyrargyrite. 
3Ag2S.Sb2S,. 

Rhombohedral.  Irregular 
massive.    Rarely  in  crystals. 

The  light  "  ruby  silver."  Charac- 
terized by  its  color  and  adamantine 
luster.  Rare,  with  associations 
like  those  of  pyrargyrite.  Easily 
Fusible  in  the  candle  flame. 

Proustite. 
SAgzS-AszS,. 

387 


NONMETALLIC 
I.     Give  a  definitely 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

Yellow- 
brown. 

Dark  brown  to 
black. 

5-5.5?     Softer  in 
some  varieties  but 
usually    harder 
than  a  knife. 

F.    Splintery.     . 

3.6-4.0 

One  good  C. 
F.     Splintery. 

43 

Brown. 

Dark  brown. 

5.5. 

One  good  C. 
F.     Uneven. 

7  2-7.5 

Light  brown. 

Light  to  dark 
brown. 

3.5 

Perfect  C.     In  6  direc- 
tions (dodecahedral). 

4.0 

Light  orange 
to  dark 
brown. 

Orange-yellow, 
brown,  black. 

4.5-5. 

Prismatic  C. 

4.8-5  2 

Light 
brown. 

Brown  to  black. 

6-7. 

F.    Uneven. 

6.8-7.1 

Light 
brown. 

Reddish  brown  to 
black. 

6-6.5. 

F.     Uneven. 
C.     Not  prominent. 

4.2 

Orange-yel- 
low. 

Deep  red  to  or- 
ange-yellow. 

4-4.5. 

C.    Basal. 

5.5 

Bright  red. 

2.5-3. 

F.    Uneven. 

5  9-6.1 

Deep  red. 

1.5-2.     Can  be 
scratched  by  fin- 
ger nail. 

F.    Conchoidal.     One 
C.,  not  prominent. 

3.5 

388 


LUSTER. 

colored  streak.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Mammillary  or  stalactitic. 

See  p.  387. 

LIMONITE 

(Bog  Iron  Ore). 
Fe4O3(OH)«= 
2Fe203.3H20. 

Mammillary  or  stalactitic. 
Radiating    groups  of 
slender  crystals. 

See  p.  387. 

Goethite. 
FeO(OH)  = 
Fe2O3.H2O. 

Monoclinic.  In  b  1  a  d  e  d 
masses. 

See  p.  379. 

Wolframite. 
(Fe,Mn)WO4. 

Isometric;  tetrahedral.  In 
granular  cleavable  masses  or 
in  rounded  crystals. 

Characterized  by  its  resinous  luster 
and  perfect  cleavage.  See  p.  379. 

SPHALERITE. 

ZnS. 

Tetragonal.  In  prismatic 
crystals;  also  massive,  com- 
pact. 

A  rare  mineral. 

Thorite. 
ThSiO4. 

Tetragonal.  In  irregular 
masses;  in  compact  fibrous 
reniform  structure;  in  rolled 
grains.  Rarely  in  prismatic 
crystals.  Commonly 
twinned. 

Very  heavy.  Usually  opaque  to 
translucent.  Occurs  as  rolled  grains 
in  sand;  in  pegmatite  veins  and  in 
granite  rocks. 

CASSITERITE 

(Tin  Stone). 
SnO2. 

Tetragonal.  In  prismatic 
crystals  vertically  striated; 
often  slender  acicular.  Fre- 
quently twinned. 

RUTILE. 
TiO2. 

Hexagonal  ;hemimorphic. 
Granular  cleavable, 

Characterized  by  its  color,  streak 
and  cleavage.  Found  at  Franklin 
Furnace,  N.  J.,  often  intimately  as- 
sociated with  franklinite  (black) 
and  willemite  (green). 

ZINCITE. 
(Zn.Mn)O. 

Monoclinic.  In  long  slender 
crystals,  often  in  interlacing 
groups. 

Characterized  by  its  color  and 
high  luster.  Decrepitates  in  the 
candle  flame. 

Crocoite. 
PbCrO4. 

Monoclinic.  Crystallized  or 
earthy. 

Easily  fusible  in  the  candle  flame. 
Characterized  by  its  color  and 
when  in  crystals  by  its  resinous 
luster. 

Realgar. 

AsS. 

NONMETALLIC 
I.     Give  a  definitely 


Streak. 

Color. 

Hardness. 

Cleavage  and 
Fracture. 

Spec. 
Grav. 

Pale  yellow. 

Lemon-yellow. 

1.5-2.     Can  be 
scratched  by  fin- 
ger nail. 

One  prominent  C. 

3.5 

Pale  yellow. 

1.5-2.5. 

F.     Conchoidal  or  un- 
even. 

2.0 

Light  yellow- 
green. 

Blackish, 
olive-green, 
brown. 

3. 

F.     Uneven. 

4.4 

Light  green. 

Dark  emerald- 
green. 

3-3.5. 

One  good  C. 

3.7 

3.5-4. 

One  good  C.,  not  com- 
monly seen. 

3.9 

Bright  green. 

3.5-4 

One   good   C.,   rarely 
seen. 

3.9-4.0 

Light  blue. 

Intense  azure-blue. 

3.5-4. 

F.     Conchoidal  or  un- 
even. 

3.7 

2.5. 

F.    Conchoidal. 

2.2 

Very  light 
blue. 

Light  green  to  tur- 
quois  blue. 

2-4. 

F.     Uneven. 

2.0-2.4 

Grayish  blue. 

Very  dark  blue. 
Bluish  green. 

1.5-2. 

One  good  C. 

2.6-2.7 

See  also  lazurite,  p.  415,  which  may  give  a  very  light  blue  streak. 


390 


LUSTER. 

colored  streak.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Monoclinic.  In  cleavable 
masses. 

Easily  fusible  in  the  candle  flame. 
Characterized  by  its  cleavage, 
color  and  resinous  luster. 

Orpiment. 

AszSs. 

Orthorhombic.  In  crystals. 
Granular  crystalline. 
Earthy. 

iurns  with  a  blue  flame  giving  a 
trong  odor  of  sulphur  dioxide.  A 
>oor  conductor  of  heat.  A  mass 
leld  in  the  hand  close  to  the  ear 
will  be  heard  to  crackle  on  account 
of  the  irregular  expansion  due  to  the 
heat  of  the  hand.  Often  earthy 
and  impure. 

SULPHUR. 

Orthorhombic.  In  aggre- 
gates of  small  crystals. 

Characterized  by  its  color  and 
small  prismatic  crystals. 

Olivenite. 
Cu(Cu.OH)AsO4. 

Orthorhombic.  In  granular 
cleavable  masses  or  in  small 
prismatic  crystals. 

Characterized  by  its  dark  green 
color  and  good  cleavage. 

Acatamite. 
Cu2Cl(OH),= 
CuCl2.3Cu(OH),. 

Orthorhombic.  In  small 
prismatic  crystals  or  in  gran- 
ular masses. 

Characterized  by  its  green  color 
and  slender  prismatic  crystals. 

Brochantite. 
CuS04.3Cu(OH)t. 

Monoclinic.  Radiating  fi- 
brous, mammillary. 

Characterized  by  its  bright  green 
color  and  radiating  fibrous  struc- 
ture. Effervesces  when  a  drop  o 
cold  acid  is  placed  on  the  specimen 

MALACHITE. 

CuC03.Cu(OH)2. 

Monoclinic.  In  small  crys- 
tals, often  in  groups.  Radi- 
ating fibrous,  mammillary. 

Characterized  by  its  intense  blue 
color.  Effervesces  when  a  drop  o 
cold  acid  is  placed  on  the  specimen 

AZURITE. 
2CuC03.Cu(OH)i. 

Triclinic.  In  crystals.  Mas- 
sive, stalactitic.  Sometimes 
with  fibrous  appearance. 

Soluble  in  water.  Metallic  taste 
Characterized  by  color.  Product 
of  oxidation  of  copper  sulphides. 

Chalcanthite. 
(Blue  Vitriol). 
CuSO4.5H2O. 

Massive  and  amorphous. 

Characterized  by  its  structure  am 
color.  Associated  with  other  cop- 
per minerals. 

CHRYSOCOLLA. 
CuSiO,.2H20. 

Monoclinic.  Usually  in  pris- 
matic crystals. 

Characterized  by  its  color  and 
streak. 

Vivianite. 
Fe3(P04),.8H20. 

and  lepidomelane,  p.  393,  which  may  give  a  light  green  streak. 


391 


NONMETALLIC 

II.     Give  a 

1.    Can  be  scratched 


Cleavage  and 
Fracture. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

Perfect  cleavage  in 
one  plane. 
The  Micas  or  re- 
lated micaceous 
minerals,  which 
possess  such  a 
perfect  cleavage 
that  they  can  be 
split  into  exceed- 
ingly thin  sheets. 
Sometimes  they  oc- 
cur as  aggregates  of 
minute  scales  when 
the  micaceous 
structure  may  not 
be  readily  appar- 
ent. 

Pale  brown,  green, 
yellow,  white. 

Vitreous,  pearly. 

2-2.5. 

2.8 

Usually    dark 
brown,   green  to 
black.     May  be 
yellow. 

Vitreous. 

2.5-3. 

3.0 

Yellowish  brown, 
green,  white. 

Vitreous,  pearly. 

2.5-3. 

2.8 

Black,    greenish 
black. 

Adamantine    to 
pearly. 

3. 

3-3.2 

Green   of   various 
shades. 

Vitreous,  pearly. 

2-2.5. 

2.7 

White  apple- 
green,  gray. 
When  impure  as  in 
soapstone,   dark 
gray,  dark  green 
to  almost  black. 

Pearly,  greasy. 

Very  soft.     Will 
leave  a  mark  on 
cloth. 

2.8 

White,  gray 
green. 

Pearly,  vitreous. 

2.5. 

2.4 

392 


LUSTER. 

colorless  streak, 
by  the  finger  nail. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Monoclinic.  In  foliated 
masses;  in  tabular  crystals 
with  hexagonal  or  diamond- 
ehaped  outlines:  in  scales. 

The  common  mica  or  ising-glass. 
Characterized  by  its  micaceous 
structure,  its  perfect  cleavage,  the 
elasticity  of  its  leaves  and  its  light 
solor.  While  in  the  mass  it  may  be 
brown  or  green,  the  thin  sheets  are 
colorless. 

MUSCOVITE 

(Potash  Mica). 
H2KAl3(SiO4),. 

Monoclinic.  In  irregular  foli- 
ated masses.  Six-sided  tab- 
ular crystals  rare. 

The  common  dark  green  or  black 
mica.  Even  in  thin  sheets  it  shows 
a  smoky  color.  Sheets  are  flexible 
and  elastic.' 

BIOTITE. 

(H,K)2(Mg,Fe), 
(Al,Fe)(Si04),. 

Monoclinic.  In  irregular  foli- 
ated masses.  Often  in  six- 
sided  tabular  crystals,  fre- 
quently large. 

Jsually  a  light-  though  sometimes 
a  dark-colored  mica.  Often  shows 
a  coppery-like  reflection  from  the 
cleavage  surface.  Occurs  kt  crys- 
talline limestone. 

PHLOGOPITE. 

(H,K)3(Mg,Fe)s 
(Al,Fe)(Si04)3. 

Monoclinic.  Usually  in 
masses  of  small  irregular 
scales. 

Characterized  by  its  micaceous 
structure  and  its  shining  black 
color. 

Lepidomelane. 
(H,K)2Fe2(Fe,Al), 
(Si04)3?. 

Monoclinic.  Usually  in  ir- 
regular foliated  masses,  at 
times  in  compact  masses  of 
minute  scales. 

Characterized  by  its  green  color 
and  by  the  fact  that  thin  sheets  are 
flexible  but  not  elastic. 

CLINOCHLORE, 

Penninite 
(Ripidolite,  Chlo- 
rite). 
H.jMg^SiA,. 

•V 

Monoclinic.  Foliated  or 
compact. 

Characterized  by  their  greasy  feel 
softness,  frequently  distinctly  foli- 
ated or  micaceous  structure.  Can- 
not be  positively  told  apart  by  phys- 
ical tests.  See  p.  280. 

TALC 

(Steatite, 
Soapstone). 
H2Mgs(Si03)4. 

PYROPHYLLITE 
H2Al2(SiO3)<. 

Rhombohedral.  Commonly 
foliated  massive.  At  times 
in  broad  tabular  crystals. 

Luster  on  cleavage  surface  pearly 
elsewhere  vitreous.  S  e  e  t  i  1  e 
Transparent  to  translucent.  Can 
be  split  with  some  difficulty  into 
thin  sheets  which  are  somewha 
flexible  but  not  elastic. 

Brucite. 
Mg(OH),. 

393 


NONMETALLIC 

II.    Give  a 

1.    Can  be  scratched 


Cleavage  and 
Fracture. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

Perfect  pinacoidal 
C.      Two  other 
cleavages  not  so 
prominent. 

Colorless,  white, 
gray.     Sometimes 
colored  by  impur- 
ities. 

Vitreous. 

2. 

2.3 

One  perfect  C. 

Blue,  bluish  green 
to  colorless. 

Pearly  to  vitreous. 

2-3. 

2.6-2.7 

Cubical  C. 

Colorless  or  white. 

Vitreous. 

2-2.5. 

2.0 

F.    Uneven. 

Pearl-gray  or  col- 
orless. Turns  to 
pale  brown  on  ex- 
posure to  light. 

Adamantine. 

2-3.      Highly  sec- 
tile. 

5.8-6.0 

F.    Uneven. 

Green  or  yellow. 

Adamantine. 

2-3.      Highly  sec- 
tile. 

5.8 

F.    Uneven. 

Pale  yellow. 

Resinous. 

1.5-2.5. 

2.0 

F.      Uneven. 
Rhombohedral  C. 
Seldom  seen. 

Colorless  or 
white. 

Vitreous. 

1.5-2. 

2.3 

F.    Conchoidal. 
C.     Prismatic,  sel- 
dom seen. 

2.1 

See  also  kaolinite,  bauxite,  and  greenockite  p  401,  which  on  account 


394 


LUSTER, 
colorless  streak, 
by  the  finger  nail.    (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Monoclinic.  In  granular 
masses  or  cleavable  crystal- 
line. 

Characterized  by  its  one  perfect 
cleavage,  and  two  others,  one  giv- 
ing a  conchoidal  surface  and  the 
other  a  silky  surface,  and  by  its 
softness. 

GYPSUM 

(Alabaster). 
CaS04.2H20. 

Monoclinic. 

See  p.  391. 

Vivianite. 
Fe3(PO4)28H2O. 

Isometric. 

See  p.  397. 

Sylvite 
KC1. 

Isometric.  In  irregular 
masses.  Rarely  in  rude 
crystals. 

Commonly  known  as  horn-silver, 
because  it  can  be  cut  with  a  knife 
like  horn  and  because  in  thin  plates 
it  is  translucent.  More  common 
than  the  other  halogen  salts  of  sil- 
ver but  to  be  distinguished  from 
them  only  by  chemical  tests. 

CERARGYRITE 

(Horn  Silver). 
AgCl. 

Isometric.  In  irregular 
masses.  Rarely  in  rude  crys- 
tals. 

Like  cerargyrite.  To  be  distin- 
guished from  it  only  by  chemical 
tests. 

Embolite. 
Ag(Cl.Br). 

Orthorhombic.  Crystal- 
lized.  Granular.  Earthy. 

Burns  with  a  blue  flame  giving  a 
strong  odor  of  sulphur  dioxide. 
Often  earthy  and  impure.  See  also 
p.  391. 

SULPHUR. 

S. 

Saline  crusts. 

Rare  minerals.  Readily  soluble  in 
water;  cooling  and  salty  tastes. 
Readily  fusible  in  the  candle  flame. 

SODA  NITER. 
NaNOs. 

Usually  in  thin  crusts,  silky 
tufts  and  delicate  acicular 
crystals. 

Niter. 
KNO,. 

of  their  earthy  structure  may  appear  to  be  softer  than  the  finger  nail. 


395 


NONMETALLIC 

II.     Give  a 

2.  Cannot  be  scratched  by  the  finger  nail, 

a.    Show  a 


Cleavage. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

Cleavage    in    one 
plane. 

See  also  the  miner- 
als of  the  mica 
group,  p.  393,  which 
may  at  times  be 
harder  than  the  fin- 
ger nail. 

Lilac,  grayish, 
white. 

Pearly. 

2.5-4 

2.8-2.9 

Pink,  gray,  white 

Pearly. 

3.5-4.5 

3.0 

Blue,  bluish  green 
to  colorless. 

Pearly  to  vitreous. 

3 

2.6-2.7 

Colorless  or  white. 

Vitreous    to    resi- 
nous. 

3.5 

4.3 

Cubic. 

i 

Colorless,     white, 
red,  blue. 

Vitreous. 

2.5 

2.1 

Colorless  or  white. 

Vitreous. 

2-2.5 

2.0 

Jin  3  directions 
at  right  angles 
to    each    other 
£     but  with  vary- 
J     ing   degrees   of 
«     ease. 
c 

Colorless,     white, 
blue,  gray,  red. 

Vitreous,  pearly. 

3-3.5. 

2.9 

U     In  3  directions 
not  at  right 
angles  to  each 
other,  giving 
rhombohe- 
drons. 

Colorless,      white 
and       variously 
tinted. 

Vitreous. 

3 

2.7 

Colorless,     white, 
pink,  etc. 

Vitreous,  pearly. 

3.5-4 

2.8 

396 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  a  cent. 

prominent  cleavage. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Monoclinic.  In  masses  of 
small  irregular  scales. 
Rarely  in  six-sided  prismatic 
crystals. 

Characterized  by  its  lilac  color. 
Always  in  very  small  sheets  or 
scales.  A  rare  mineral  often  asso- 
ciated with  colored  tourmalines. 

Lepidolite 
(Lithia  Mica). 
LiK(AJ(OH,F)2) 
Al(SiO,)8. 

Monoclinic.  Usually  in  ir- 
regular foliated  masses. 

Folia  somewhat  brittle.  Charac- 
terized by  its  color.  A  rare  min- 
eral. 

Margarite. 
H2CaAl4Si,Oi,. 

Monoclinic.  Prismatic  crys- 
tals, often  in  stellate  groups. 
At  times  divergent,  fibrous 
or  earthy. 

A  rare  mineral. 

Vivianite. 
Fe3(PO4)2.8H,O. 

Usually  massive  with  radia- 
ting structure. 

Cleavage  rarely  prominent.  See  p. 
411. 

WITHERITE. 
BaCOj. 

Isometric.  In  granular 
cleavable  masses  or  in  cubic 
crystals. 

Common  salt.  Characterized  by 
its  salty  taste.  Fusible  in  the  can- 
dle flame.  Highly  diathermous. 
Compare  sylvite,  below. 

HALITE 

(Common  Salt). 

NaCl. 

Isometric.  Same  as  for  hal- 
ite. Crystals  frequently 
show  octahedral  truncations. 

A  rare  mineral  closely  resembling 
halite.  To  be  distinguished  from 
it  by  its  more  bitter  taste  and  its 
greater  softness  (can  usually  be 
scratched  by  the  finger  nail). 

Sylvite. 
KC1. 

Orthorhombic.  In  granular 
cleavable  masses. 

Characterized  chiefly  by  its  cleav- 
age. If  hi  a  form  where  this  does 
not  show  it  wijl  require  chemical 
tests  to  determine  it. 

ANHYDRITE. 
CaS04. 

Rhombohedral.  In  fine-  to 
coarse-grained  cleavable 
masses.  Whan  crystallized 
shows  prismatic,  rhombo- 
hedral  and  scalenohedral 
forms. 

Effervesces  readily  when  a  drop  of 
cold  acid  is  placed  upon  it.  Char- 
acterized by  its  perfect  rhombo- 
hedral  cleavage  and  crystal  forms. 
Clear  varieties  show  strong  double 
refraction.  Occurs  in  large  masses 
as  limestone  and  marble.  Crystal 
faces  may  be  harder  than  a  cent. 

CALCITE. 
CaCO,. 

Rhombohedral 

See  p.  407. 

DOLOMITE. 

CaMg(CO,),. 

397 


NONMETALLIC 

II.     Give  a 

2.  Cannot  be  scratched  by  the  finger  nail, 

a.     Show  a 


Cleavage  and 
Fracture. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

In  3  directions 
giving    tabular 
diamond-shaped 
cleavage  blocks. 

Colorless,  white, 
blue,  yellow,  red. 

Vitreous,  pearly. 

3-3.5 

4.5 

Colorless,  white, 
blue,  red. 

Vitreous,  pearly. 

3-3.5 

3.9 

Colorless  or  white. 
Gray  and  brown 
when  impure. 

Adamantine. 

3 

6.3 

6.     Do  not  show  a 
1.     A  small  splinter  is 

a.  Readily  soluble  in  water; 


F.    Conchoidal. 

Colorless,     white, 
red. 

Vitreous,  greasy. 

2.5 

1.6 

F.    Conchoidal. 
One  good  C.  sel- 
dom seen. 

Colorless  or  white. 

Vitreous. 

2-2.5 

1.7  • 

F.    Conchoidal. 

Colorless  or  white. 

Vitreous. 

2-2.5 

1.7 

See  also  halite,  p.  397,  which  may  exist  in  forms  in  which  its  cleavage  is 


398 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  a  cent. 

prominent  cleavage.     (Continued.} 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Orthorhombic.  In  aggregates 
of  platy  crystals  or  in  tabular 
orthorhombic  crystals  with 
rectangular  or  diamond- 
shaped  outlines.  Crystal 
edges  frequently  beveled  by 
other  faces.  At  times  granu- 
lar. 

Characterized  by  its  unusual 
weight  for  a  nonmetallic  mineral, 
its  platy  structure,  cleavage  and 
pearly  luster  on  basal  cleavage. 
At  times  to  be  told  from  celestite 
and  anglesite  only  getting  a  green 
flame  (test  for  barium). 

BARITE, 

Barytes. 
(Heavy  Spar). 
BaSO4. 

Orthorhombic.  In  granular 
platy  masses  or  in  tabular 
crystals  like  those  of  barite. 
At  times  in  long  prismatic- 
like  crystals  with  blunt  ter- 
minations. 

Very  similar  in  appearance  to  ba- 
rite. Frequently  can  only  be  told 
from  barite  and  anglesite  by  get- 
ting a  crimson  flame  color  (test  for 
strontium). 

CELESTITE. 

SrSO4. 

Orthorhombic.  Usually 
earthy  and  impure.  At 
times  in  small  crystals  re- 
sembling those  of  barite  and 
celestite. 

Characterized  by  its  weight.  Usu- 
ally associated  with  galena  as  an 
alteration  product  in  concentric 
layers  around  an  unaltered  core  of 
galena.  Will  often  need  a  test  for 
lead  for  its  positive  identification. 

ANGLESITE. 

PbS04. 

prominent  cleavage. 
fusible  in  the  candle  flame. 

yield  a  taste. 


Orthorhombic.  Commonly 
massive,  granular. 

A  rare  mineral.  In  the  candle 
flame  swells,  then  fuses.  Bitter 
salty  taste. 

Carnallite. 
MgCl2.KCl.flH2O. 

Monoclinic.  In  crusts,  often 
impure.  Rarely  in  prismatic 
crystals. 

A  comparatively  rare  mineral. 
Found  only  in  dry  countries.  In 
candle  flame  swells  and  then  fuses. 
Sweetish-alkaline  taste. 

BORAX. 
Na2B4O7.10H2O. 

Usually  fibrous  or  massive 
or  in  mealy  or  solid  crusts. 

Easily  fusible  with  frothing  in  can- 
dle flame.  A  rare  mineral.  As- 
tringent taste. 

Kalinite 
(Potash  Alum). 
KA1(SO4)2.12H2O. 

obscure,  and  chalcanthite,  p.  390,  which  may  give  a  nearly  colorless  streak. 


NONMETALLIC 

n.     Give  a 

2.  Cannot  be  scratched  by  finger  nail, 

b.     Do  not  show  a 
1.    A  small  splinter  is  fusible 

b.  Insoluble  in 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

Colorless  or  white. 

Vitreous  to  greasy. 

F.     Uneven. 
C.    In  one  direc- 
tion, seldom  seen. 

3-3.5 

2.9 

Adamantine. 

F.    Conchoidal. 

3-3.5 

6.5 

'Colorless,  yellow, 
orange,  brown. 

Resinous. 

F.    Uneven. 

3-3.5 

7.0-7.2 

See  also  vanadinite  below, 


2.    Infusible 


Colorless  or  white. 
See  also  bauxite, 
wavellite  and  ser- 
pentine below, 
which  may  be 
nearly  white. 

Vitreous    to    resi- 
nous. 

F.     Uneven. 

3-3.5 

4.3 

Pearly,  dull. 

F.    Earthy. 

2-2.5 

2.6 

Honey-,   citron-  or 
orange-yellow. 

Adamantine,  resi- 
nous, earthy. 

F.     Uneven. 

3-3.5 

4.9-5.2 

Yellow,  brown, 
gray,  white. 

Dull,  earthy. 

F.    Uneven. 

3 

2.5 

Ruby-red,  brown, 
yellow. 

Resinous. 

F.  Uneven. 

2 

6.9-7.1 

400 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  a  cent. 

prominent  cleavage. 
in  the  candle  flame. 

water. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Monoclinic.  Massive. 

Characterized  by  its  peculiar  trans- 
lucent appearance,  like  that  of  par- 
affine.  Its  fine  powder  practically 
disappears  when  placed  in  water 
but  is  insoluble. 

CRYOLITE. 

Na3AlF6. 

Orthorhombic.  In  granular 
masses;  platy  crystals  often 
crossing  each  other  to  form  a 
lattice-like  effect. 

When  fused  in  the  candle  flame  is 
slowly  reduced  showing  globules 
of  lead  on  surface  of  fragment. 
Heavy.  Effervesces  when  a  drop 
of  cold  acid  is  placed  upon  it. 
Associated  usually  with  galena. 

CERUSSITE. 
PbCO3. 

See  p.  413. 

Mimetite. 
Pb4(PbCl)(AsO4)3. 

which  may  fuse  slightly. 


in  the  candle  flame. 


Often  massive  with  radiat- 
ing structure. 

See  p.  411. 

WITHERITE. 
BaCOj. 

Generally  clay-like,  com- 
pact or  mealy. 

Often  impure.  When  breathed  upon 
gives  an  argillaceous  odor.  Will 
adhere  to  a  dry  tongue.  The  basis 
of  most  clays. 

KAOLINITE. 

H4Al2Si20,. 

Hexagonal,  hemimorphic. 
Usually  in  form  of  powder. 
Rarely  in  crystals. 

A  rare  mineral.  Characterized  by 
its  color  and  pulverulent  form. 
Often  as  a  coating  on  sphalerite. 

Greenockite. 
CdS. 

In  rounded  grains.  Also 
earthy,  clay-like. 

A  rare  mineral.  Often  impure. 

Bauxite. 
A12O(OH)4. 

Hexagonal,  pyramidal.  In 
slender  prisms.  Sometimes 
in  cavernous  crystals  and 
also  in  rounded  barrel-shaped 
forms. 

Characterized  by  its  color  and 
crystals.  Compare  mimetite, 
above  and  pyromorphite,  p.  413. 

Vamu  Unite. 
Pb^PbClHVO*)!. 

401 


NONMETALLIC 

II.     Give  a 

2.   Cannot  be  scratched  by  the  finger  nail, 

b.     Do  not  show  a 
2.     Infusible 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

Yellow,  green, 
white,  brown. 

Vitreous,  pearly. 

F.     Uneven.    One 
C.,  not  prominent. 

3-4 

2.3 

Olive  to  blackish- 
green,  yellow-green, 
white. 

Greasy-,  wax-like. 

F.     Uneven. 

3.5-5 

2.6 

Pale  to  deep  green. 

Dull  to  resinous. 

F.    Uneven. 

3-4 

2.2-2.8 

Some  varieties  of  anglesite,  p.  399,  anhydrite,  p.  397,  and  vivianite,  p.  397,  do  not  show 

3.   Cannot  be  scratched  by  a  cent 

a.     Show  a 


Cleavage. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

«     C.    Pinacoidal. 

Blue,    usually 
darker  at  center  of 

Vitreous,  pearly. 

5-7 

3.6 

5 

crystal.    At  times 

1 

white,  gray  or 

O 

green. 

$ 
«  >,C.    Basal. 

Light  blue,  green, 

Resinous. 

4.5-5 

3.5 

Ctf  "rt 

gray,  salmon  to 

i° 

clove-brown. 

y 

g     C.    Pinacoidal. 

White,  yellow, 

Pearly,  vitreous. 

3.5-4 

2.1-2.2 

1 

brown,  red. 

402 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  a  cent. 

prominent  cleavage. 

in  the  candle  flame.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Usually  in  radiating  hemi- 
spherical, globular  forms. 

Characterized  by  its  structure. 

Wavellite. 
(A1.0H)3(PO4)2 
5H2O. 

Massive.  Fibrous. 

See  p.  415. 

SERPENTINE. 

H4Mg3Si209. 

Massive  and  amorphous,  at 
times  as  an  incrustation  with 
botryoidal  or  stalactitic  sur- 
face; earthy. 

A  rare  mineral.     Characterized 
chiefly  by  its  color. 

Genthite 
(Garnierite). 
Nickel,    magnesium 
silicate. 

a  distinct  cleavage  and  might  be  expected  to  be  included  in  the  above  group. 

but  can  be  scratched  by  a  knife. 

prominent  cleavage. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Triclinic.  In  bladed  s  t  r  u  c- 
ture  with  prominent  cleavage 
plane. 

Characterized  by  its  color  and  the 
Fact  that  it  can  be  scratched  by  a 
knife  in  a  direction  parallel  to 
length  of  crystal  but  not  in  a  direc- 
tion at  right  angles  to  this. 

CYANITE. 

Al2SiO6. 

Commonly  massive  cleav- 
able. 

Rare  species.  Triphyllite  is  essen- 
tially LiFePO4  and  lithiophyllite 
LiMnPO4. 

Triphyllite- 
Lithiophyllite. 
Li(Fe,Mn)PO4. 

Monoclinic.  Commonly  in 
sheaf-like  aggregates  of  crys- 
tals or  in  flat  tabular  crys- 
tals. 

Characterized  by  the  grouping  of 
its  crystals  into  a  radiating  sheaf- 
like  aggregate  and  by  the  pearly 
luster  of  the  cleavage  face. 

STILBITE. 
H.(Ca,Nai)Al, 
(SiO8),.4H,O. 

403 


NONMETALLIC 

II.     Give  a 

3.    Cannot  be  scratched  by  a  cent, 

a.    Show  a 


Cleavage. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

C.    Basal. 

Colorless, 
white,  pale 
green,  yellow, 
rose. 

Pearly,  vitreous. 

4.5-5 

2.3-2.4 

C.    Pinacoidal. 

White,  yellow, 
red. 

Pearly,  vitreous. 

3.5-4 

2.2 

g   .C.    Pinacoidal, 
J5  2  often  not  prom- 
&  -*  inent. 
Jo. 
| 

.as 

White, 
colorless. 

i 

* 

Vitreous. 

4.5 

2.4-2.5 

<D  = 

«?'£  C.    Pinacoidal. 

C"5 

3     Colorless, 
w     white. 

B 

Vitreous. 

4-4.5 

2.4 

1 
fl^C.    Pinacoidal, 
q     seldom  seen. 

8     Colorless, 
t    white. 

Vitreous    to    resi- 
nous. 

3.5 

4.3 

£     C.    Pinacoidal. 

&     Colorless, 
white,  gray. 

Vitreous,  pearly. 

5-5.5 

2.8-2.9 

C.    Pinacoidal, 
also  basal   but 
seldom  seen. 

Colorless, 
white,  gray. 

Vitreous,  pearly. 

4.5-5 

2.7-2.8 

C.     In  two  di- 
rections. 
C.     Prismatic. 

Colorless, 
white. 

Vitreous. 

5-5.5 

2.2 

404 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  a  knife. 

prominent  cleavage.     (Continued.} 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Tetragonal.  In  prismatic 
crystals  with  square  cross- 
section.  Often  resemble  a 
combination  of  cube  and  oc- 
tahedron. 

Pearly  luster  on  basal  plane  (cleav- 
age face),  vitreous  luster  on  other 
faces.  Prism  faces  usually  verti- 
cally striated.  A  zeolite  found 
lining  cavities  in  igneous  rocks. 

APOPHYLLITE. 
H7KCa4(Si03), 
4*H20. 

Monoclinic.  Crystals  often 
tabular  parallel  to  cleavage 
plane  (surface  of  pearly  lus- 
ter). 

Pearly  luster  on  cleavage  face, 
elsewhere  vitreous.  A  rare  zeo- 
lite found  lining  cavities  in  igneous 
rocks. 

Heulandite. 
H4(Ca,Na,)Al, 
(SiO^.SHjO. 

Monoclinic.  Crystals  usu- 
ally like  square  prisms  ter- 
minated by  4  pyramid  faces, 
the  latter  faces  striated.  At 
times  in  cruciform  penetra- 
tion twins. 

Characterized  by  its  crystals,  see 
p.  267.  A  rare  zeolite  found  lining 
cavities  in  igneous  rocks. 

Harmotone. 
(Ba,K2)Al2Si60M 
5H2O. 

Monoclinic.  In  crystalline  or 
granular  crystalline  masses. 

Decrepitates  violently  in  the  can- 
dle flame.  A  rare  mineral. 

Colemanite. 
CajBjOn.SHjO. 

Usually  massive  with  .radi- 
ating structure. 

Seep.  411. 

WITHERITE. 

BaCO3. 

Monoclinic.  Usually  cleav- 
able  massive  to  fibrous. 
Also  compact.  Rarely  in 
tabular  crystals. 

Associated  with  crystalline  lime- 
stone. 

WOLLASTONITE. 
CaSiOj. 

Monoclinic.  Commonly  in 
close  radi  tin?  aggregates  of 
acicular  crystals  Fibrous 
massive. 

Characterized  by  its  radiating 
structure.  A  rare  mineral. 

Pectolite. 
HNaCMSiO,),. 

Orthorhombic.  In  slender 
to  acicular  prismatic  crystals 
terminated  by  4  low  pyra- 
mid faces.  Prism  faces  ver- 
tically striated.  Often  in 
radiating  groups. 

Characterized  chiefly  by  its  struc- 
ture. A  zeolite  found  lining  cavi- 
ties in  igneous  rocks. 

NATROLITE. 

NasAKAlO) 
(Si6,),.2H,0. 

405 


NONMETALLIC 

II.     Give  a 

3.   Cannot  be  scratched  by  a  cent, 

a.     Show  a 


Cleavage. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

C.      Prismatic 
making    angles 
of  55°  and  125°. 

5!. 

White,  green, 
black. 

Vitreous,  pearly. 

5-6 

3.0-3.3 

J.fc.      Prismatic 
u  "o  making    angles 
«  |of  54°  and  126°. 

Gray,  clove- 
brown,  green. 

Vitreous,  pearly. 

5-6 

3.1 

OT3 

>  §C.     Prismatic, 
*"*  2  rather  poor  at 
.9-|  90°  angles. 

tP 
.3 

v  o 

3| 
1 

White,    green, 
black. 

Vitreous. 

5-6 

3.1-3.5 

C.      Prismatic 
with  nearly  90° 
angles. 

Rose-red,  pink, 
brown. 

Vitreous. 

5-6 

3.6 

^     In  3  directions 
«     not  at  right  an- 
^     gles  to  each 
£     other,  giving 
rhombohe- 
•9     drons. 

1 

Colorless,   white 
and   variously 
tinted. 

Vitreous. 

3 

2.7 

Colorless,  white, 
pink,  etc. 

Vitreous,  pearly. 

3.5-4 

2.8 

406 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  a  knife. 

prominent  cleavage.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Monoclinic.  In  slender  pris- 
matic crystals,  showing  prom- 
inent cleavage,  giving  fre- 
quently a  bladed  appearance. 
When  terminated  the  crys- 
tals usually  show  2  low  dome 
faces.  Sometimes  fibrous, 
asbestiform. 

Tremolite,  CaMg3Si4O12,  is  white, 
gray,  violet;  ActinoJite, 
Ca(Mg,Fe)4Si4O12)  green  of  various 
shades;  Amphibole  or  Horn- 
blende,  CaMg3Si4O12  with  NajAlj 
Si4O12  and  Mg2Al4Si4O12,  is  green  to 
black.  The  group  is  characterized 
chiefly  by  its  broad  angle  cleavage. 
Found  in  metamorphic  rocks. 

AMPHIBOLE 
GROUP. 

Essentially  calcium, 
magnesium  metasil- 
icates. 

Orthorhombic.  Lamellar  or 
fibrous. 

Seep.  419. 

Anthophyllite. 
(Mg,Fe)Si03. 

Monoclinic.  In  stout  pris- 
matic crystals  with  rectan- 
gular  cross-section.  When 
terminated  they  usually 
show  more  than  2  faces  at 
ends.  Often  in  granular  crys- 
talline masses. 

Diopside,  CaMgSi2O6,  is  colorless, 
white,  pale  green;  Pyroxene, 
Ca(Mg,Fe)Si2O6,  light  to  dark 
green;  A  u  g  i  t  e,  CaMgSi2O«  with 
MgAl2SiO6  and  NaAlSi2O6,  is 
greenish  black  to  black.  Charac- 
terized by  the  rectangular  cross- 
section  of  its  crystals  and  the  rather 
poor  prismatic  cleavage  at  right 
angles.  Shows  at  times  a  basal 
parting.  Found  in  igneous  rocks. 

PYROXENE 
GROUP. 

Essentially  calcium, 
magnesium  metasil- 
cates. 

Triclinic.  Usually  massive, 
cleavable  to  compact,  in 
embedded  grains;  in  large 
rough  crystals  with  rounded 
edges. 

Characterized  by  its  color. 

Rhodonite. 
MnSiO,. 

Rhombohedral.  In  granular 
cleavage  masses  or  crystal- 
lized. 

See  p.  397. 

CALCITE. 

CaCO,. 

Rhombohedral.  In  fine-  to 
coarse-grained  cleavable 
masses.  Often  in  strongly 
curved  rhombohedral  crys- 
tals. 

Will  not  effervesce  when  a  drop  of 
cold  hydrochloric  acid  is  placed 
upon  it.  Characterized  by  its 
rhombohedral  cleavage,  by  its 
rounded  rhombohedral  crystals 
and  its  frequently  pink  or  flesh 
color.  Pearly  luster  on  curved 
crystal  faces.  Occurs  in  iarge 
masses  as  dolomite  limestone  and 
marble.  Frequently  associated 
with  lead  and  zinc  minerals. 

DOLOMITE. 

CaMg(CO,)2. 

407 


NONMETALLIC 

II.     Give  a 

3.   Cannot  be  scratched  by  a  cent, 

a.     Show  a 


Cleavage. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

In  3  directions  not 
at  right  angles  to 
each  other,  giving 
rhombohedrons. 

White,  yellow, 
gray,  brown. 

Vitreous. 

3.5-4 

3.0-3.1 

Light  to  dark 
brown. 

Vitreous,  pearly. 

3.5-4 

3.8 

Pink,  rose-red, 
dark  red,  brown. 

Vitreous,  pearly. 

3.5-4.5 

3.5-3.6 

Brown,  green, 
blue,  pink,  white. 

Vitreous. 

5 

4.3 

White,  yellow, 
flesh-red. 

Vitreous. 

4-5 

2.1 

In  3  directions    at 
right  angles  to  each 
other  but  with 
varying  degrees  of 
ease. 

Colorless,     white, 
blue,  gray,  red. 

Vitreous,  pearly. 

3-3.5 

2.9 

In  3  directions  giv- 
ing tabular  dia- 
mond-shaped cleav- 
age blocks. 

Colorless,     white, 
blue,  yellow,  red. 

Vitreous,  pearly. 

3-3.5 

4.5 

C.    Octahedral. 

Colorless,     violet, 
green,     yellow, 
pink.    Usually  has 
a  fine  color. 

Vitreous. 

4 

3.1 

C.    Perfect  in  6  di- 
rections,    dodeca- 
hedral. 

Yellow,  brown, 
white. 

Strongly  resinous. 

3.5-4 

4.0 

Dodecahedral     C., 
more   or    less    dis- 
tinct. 

White,  gray,  blue, 
green. 

Greasy,  vitreous. 

5.5-6 

2.1-2.3 

Note.  —  Apatite,  p.  413,  may  show  somewhat  imperfect  cleavage. 

408 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  a  knife. 

prominent  cleavage.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Rhombohedral.  In  granu- 
lar cleavable  masses. 

A  rare  mineral. 

Magnesite. 
MgC03. 

Rhombohedral.  In  cleav- 
able masses  or  in  small 
rhombohedral  crystals. 

After  being  heated  in  the  candle 
flame  a  fragment  is  attracted  by  a 
magnet. 

SIDERITE. 

FeC03. 

Rhombohedral.  In  cleav- 
able masses  or  in  small 
rounded  rhombohedral  crys- 
tals. 

Characterized  by  its  color,  cleav- 
age and  softness. 

RHODOCHRO- 
SITE. 
MnCO3. 

Rhombohedral.  Usually  in 
botryoidal  or  honey-combed 
masses. 

See  p.  411. 

SMITHSONITE. 
ZnCO3. 

Rhombohedral.  In  small 
rhombohedral  crystals  with 
nearly  cubic  angles. 

A  zeolite  found  lining  cavities  in 
igneous  rocks. 

CHABAZITE. 

(Ca,Na2)Al2 
(Si03)46H20. 

Orthorhombic.  In  granular 
cleavable  masses. 

See  p.  397. 

Anhydrite. 
CaSO4. 

Orthorhombic.  In  tabular 
crystals  and  lamellar  masses. 

See  p.  399. 

BARITE, 

Barytes 
(Heavy  Spar). 
BaSO4. 

Isometric.  In  cubic  crystals, 
often  in  interpenetration 
twins. 

Characterized  by  its  crystals,  color 
and  cleavage.  The  bluish  green 
variety  shows  fluorescence,  i.e.  ap- 
pears green  by  transmitted  and 
blue  by  reflected  light. 

FLUORITE. 

CaF2. 

Isometric,  tetrahedral.  In 
cleavable  masses  or  small 
ronnded  crystals. 

Characterized  by  its  color,  luster 
and  cleavage. 

SPHALERITE. 

ZnS. 

Isometric.  Massive  or  in 
embedded  grains. 

Frequently  blue  in  color.  A  rock- 
making  mineral,  never  associated 
with  quartz.  Usually  opaque  to 
translucent. 

Sodalite. 
Na4(AlCl)Al, 
(Si04),. 

409 


NONMETALLIC 

II.     Give  a 

3.   Cannot  be  scratched  by  a  cent, 

6.     Do  not  show  a 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

>>        Colorless, 
§        pale  green, 
ti        yellow. 
A 

.a 

ifl 

Vitreous. 

F.     Uneven. 

5-5.5 

2.9-3.0 

£ 

5        White,  pale 
•A        green,  blue. 

Vitreous. 

F.      Uneven.      C. 
prismatic,   seldom 
seen. 

4.5-5 

3.4 

.-§        White,  gray, 
oj  „;     light  green, 
§".2     darker  green 
gj  "8     or  brown. 

if 

Vitreous  to  dull. 

F.      Uneven.      C. 
prismatic,  seldom 
seen. 

5-6 

2.7 

^|     Colorless    or 
i  f     white. 

°S 

•*! 

Vitreous. 

F.     Uneven. 

3.5-4 

2.9 

o  — 
•1J2     Colorless    or 
J§     white. 
.a 

Rj 

Vitreous. 

F.    Uneven. 

5-5.5 

2.3 

|| 

13  °     Colorless    or 
^        white. 

s 

Vitreous  to 
resinous. 

F.     Uneven. 

3.5 

4.3 

J5        Colorless    or 
.0        white. 

6 

Vitreous,  pearly. 

Pinacoidal    C., 
may  be  obscure. 

4.5-5 

2.7-2.8 

g        Colorless    or 
white. 

Vitreous. 

Prismatic  C.,  may 
be  obscure. 

5-5.5 

2.2 

Brown,  green, 
fblue,  pink, 
g    white. 

H 

Vitreous. 

F.    Uneven. 
Rarely  shows 
rhombohedral  C. 

5 

43 

§     Gray,  brown 
p     green,  yel- 
low. 

Resinous,   ada- 
mantine. 

F.    Uneven.    Pris- 
matic C.,  seldom 
prominent. 

5-5.5 

3  4-3.5 

410 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  a  knife. 

prominent  cleavage. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Monoclinic.  Usually  in  crys- 
tals developed  with  nearly 
equal  dimensions  in  all  di- 
rections and  many  faces. 

Characterized  by  its  luster  and 
crystals.  Usually  transparent. 
Occurs  with  the  zeolites,  lining  cav- 
ities in  igneous  rocks. 

DATOLITE. 
Ca(B.OH)SiO4. 

Orthorhombic.  Often  in  ra- 
diating crystal  groups.  Also 
stalactitic,  mammillary. 

Characterized  by  its  structure. 
Pyroelectric. 

CALAMINE. 
(Zn.OH)2SiO,. 

Tetragonal.  In  prismatic 
crystals,  granular  or  mas- 
sive. 

Often  altered. 

SCAPOLITE. 
Ca4Al6Si6Oi8  with 
Na4Al3Si9O34Cl. 

Orthorhombic.  Frequently 
in  radiating  groups  of  acicular 
crystals. 

Effervesces  in  cold  acids.  Falls 
to  powder  in  candle  flame. 

ARAGONITE. 

CaCO3. 

Isometric.  In  crystals,  usu- 
ally trapezohedrons. 

Characterized  by  its  crystals  and 
its  glassy  luster.  A  zeolite  found 
lining  cavities  in  igneous  rocks. 

ANALCITE. 
NaAl(SiO3)2H,O. 

Orthorhombic.  Often  in 
masses  with  radiating  struc- 
ture; granular;  rarely  in  hex- 
agonal pyramidal  crystals. 

Heavy.  When  a  fragment  is  placed 
in  cold  hydrochloric  acid  there  is  a 
brisk  effervescence  for  a  moment 
and  then  the  action  ceases. 

WITHERITE. 

BaCO3. 

In  radiating  acicular  crys- 
tals. 

See  p.  405. 

Pectolite. 
HNaCa2(SiO3)3. 

Radiating  prismatic. 

See  p.  405. 

Natrolite. 
NajAKAlO) 
(SiO3),.2H,O. 

Rhombohedral.  In  rounded 
botryoidal  forms.  Often  in 
honey-combed  masses. 

Harder  than  most  carbonates.  A 
fragment  effervesces  when  placed 
in  cold  hydrochloric  acid. 

SMITHSONITE. 

ZnCO3. 

Monoclinic.  In  thin  crystals 
with  sharp  edges,  wedge- 
shaped. 

Characterized  by  its  crystals. 

TITANITE 

(Sphene). 
CaTiSiO». 

411 


NONMETALLIC 

II.     Give  a 

Cannot  be  scratched  by  a  cent, 

b.     Do  not  show  a 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

Yellowish  to 
.     reddish 
^     brown. 

•3 

Resinous,     vitre- 
ous. 

F.    Uneven.    Pris- 
matic C.,  seldom 
prominent. 

4-5 

5.0 

j£    Yellowish  to 
i-g.    reddish 
S  3     brown. 

Resinous. 

F.    Uneven. 

5-5.5 

5.2-5.3 

!  |    White,  yel- 
ls T5     low,  green, 
'g  |     brown. 

Vitreous,  ada- 
mantine. 

F.     Uneven. 

4.5-5 

6.0 

•||     Usually  a 
3*     brilliant 
pj  a     shade  of  yel- 
3     low  or  orange. 
££     Also  red, 
—  8     gray,  green. 
«« 

Vitreous    to    ada- 
mantine. 

F.     Uneven. 

4.5-5 

6.0 

•§ 
a'i     Colorless, 
§  §*    yellow,  or- 
^  8     ange,  brown. 

Resinous. 

F.     Uneven. 

3.5 

7.0-7.2 

Yellow, 
brown,  gray, 
white. 

Dull,  earthy. 

F.     Uneven. 

3 

2.5 

White,  green, 
black. 

Vitreous. 

F.         Uneven. 
Rather  poor  pris- 
matic  C.,   at   90° 
angles. 

5-6 

3.1-3.5 

So    Green,    blue, 
>,    violet,  brown, 
5|     colorless. 

Vitreous,  greasy. 

F.     Uneven. 

5 

3.1 

Green, 
brown, 
yellow,  gray. 

Resinous. 

F.     Uneven. 

3.5-4 

6.5-7.1 

412 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  a  knife. 

prominent  cleavage.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Tetragonal.  In  prismatic  or 
pyramidal  crystals.  In 
rolled  grains. 

A  rare  mineral.     Heavy. 

Xenotime. 
YPO4. 

Monoclinic.  In  small  crys- 
tals or  as  rolled  grains. 

A  rare  mineral.    Heavy. 

MONAZITE. 
(Ce,La,Di)P04 
often  with  ThSiO4. 

Tetragonal.     In  octahedral- 
like  crystals.    Massive, 
granular. 

A  rare  mineral.    Heavy. 

Scheelite. 
CaW04. 

Tetragonal.  Usually  in  very 
thin  square  tabular  crystals. 
Less  frequently  octahedral 
in  habit.  Also  granular 
massive. 

Characterized  by  its  crystals  and 
color.    Heavy. 

Wulfenite. 
PbMoO4. 

Hexagonal.  In  small  pris- 
matic crystals.  Prism  faces 
often  curved,  giving  barrel 
shapes.  In  granular  masses. 

A  rare  mineral.      Heavy.      Fuses 
slowly  in  candle  flame. 

Mimetite. 
Pb4(PbCl)(As04)a. 

See  p.  401. 

Bauxite. 
A120(OH)4. 

Monoclinic.  In  stout  rec- 
tangular crystals  with  rec- 
tangular cross-section. 

See  p.  407. 

PYROXENE 
GROUP. 

Essentially  calcium 
and  magnesium  sili- 
cates. 

Hexagonal.  In  prismatic 
crystals,  often  large,  usually 
with  prominent  pyramid 
planes.  Also  massive. 

Characterized  by  its  crystals. 

APATITE. 
Ca4(CaF)(PO4),. 

Hexagonal.  In  small  crys- 
tals. Often  in  rounded  barrel- 
shaped  forms.  Crystals  at 
times  cavernous.  Often 
globular  and  botryoidal. 

Characterized  chiefly  by  its  struc- 
ture and  color.     Heavy. 

PYROMOR- 
PHITE. 
Pb4(PbCl)(P04),. 

413 


NONMETALLIC 

II.    Give  a 

3.    Cannot  be  scratched  by  a  cent, 

b.    Do  not  show  a 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

Yellow, 
.     green,  white, 
£     brown. 

Vitreous,  pearly. 

F.  Uneven.  One 
C.,  not  prominent. 

3-4 

2.3 

3 
§     Olive  to 
•g     blackish 
j8     green,  yellow- 
g    green,  white. 

si 

Greasy,  waxlike. 

F.  Uneven. 

3.5-5 

2.6 

£-2 
0$;s     Yellow-green, 
t^a    white,  color- 
s' |j     less,    blue, 
6     gray,  brown. 

l| 

Vitreous. 

F.  Uneven.  May 
show  fairly  good 
C. 

5.5 

4.0-4.1 

1 

J     White,  gray, 
.•£    blue,  green. 

9 

« 

Greasy,  vitreous. 

F.    Conchoidal. 
Dodecahedral   C., 
seldom  seen. 

5.5-6 

2.1-2.3 

1 

™     Deep  azure- 
«     blue,     green- 
"    ishblue. 

Vitreous. 

F.  Uneven. 

5-5.5 

2.4 

NONMETALLIC 

II.     Give  a 

4.   Cannot  be  scratched  by  a  knife, 

a.     Show  a 


Cleavage. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

8,    C.    Basal. 

• 
> 

? 

White    to    pale 
green  or  blue. 

Vitreous  to  greasy. 

6 

3.0 

1 

g     C.    Pinacoidal. 

O 

Colorless,     white, 
gray. 

Vitreous,  pearly. 

5-5.5 

2.8-2.9 

414 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  a  knife. 

prominent  cleavage.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Usually  in  radiating  hemi- 
spherical, globular  forms. 

Characterized  by  its  structure. 

Wavellite. 
(A1.0H)3(P04)2 
5H2O. 

Massive.  Fibrous  in  the  as- 
bestos variety. 

Characterized     by     its     massive 
structure,  mottled  green  color  and 
frequently  by  the  presence  of  veins 
of  finely  fibrous  material,  known  as 
chrysotile  or  asbestos. 

SERPENTINE. 
H4Mg3Si209. 

Massive  and  in  disseminated 
grains. 

See  p.  423. 

WILLEMITE. 

Zn2SiO4. 
Troostite. 
(Zn,Mn)2SiO4. 

Massive  or  in  embedded 
grains. 

See  p.  409. 

Sodalite. 
Na4(AlCl)Al2 
(Si04)3. 

Usually  massive. 

Characterized  by  its  color. 

Lazurite 
(Lapis-Lazuli). 
(Na2,Ca)2(Al.NaS,) 
Alj(SiO4),. 

LUSTER. 

colorless  streak. 

but  can  be  scratched  by  quartz. 

prominent  cleavage. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Usually  cleavable  to  com- 
pact massive. 

A    rare    mineral.     Usually    found 
with  lepidolite,  tourmaline,  etc. 

Amblygonite. 
Li(AlF)PO4. 

Usually  cleavable  massive 
to  fibrous. 

See  p.  405. 

WOLLASTONITE. 
CaSiO,. 

415 


NONMETALLIC 
II.    Give  a 

4.    Cannot  be  scratched  by  a  knife, 

a.    Show  a  prominent 


Cleavage. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

.     C.    Pinacoidal 

White,  gray,  pale 
lavender,    yellow- 

Pearly, vitreous. 

6.5-7 

3.4 

1 

ish,  greenish. 

3 

£    C.    Pinacoidal 

Grayish    white, 

Vitreous,  pearly. 

6-6.5 

3.3 

5 

green,  pink. 

1 

2     C.    Pinacoidal 

Hair-  brown,  gray, 

Vitreous. 

6-7 

3.2 

1 

grayish  green. 

1 

$ 

C.    Basal. 

Yellowish    to 

Vitreous. 

6-7 

3  4 

t* 

Dlackish  green  to 

gray. 

a     C.    Pinacoidal. 

Blue,    usually 
darker  at  center  of 
crystal.    At  times 
gray  or  green. 

Vitreous,  pearly. 

5-7 

3.6 

Cleavage      in 
two  directions. 

Colorless,  white. 

Vitreous. 

5-5.5 

2.2 

C.    Prismatic. 

»     C.      Basal  and 
§     pinacoidal 

Colorless,     white, 
gray,  cream,  red, 

Vitreous,  pearly. 

6 

2.6 

.2     making    a    90° 

green. 

ft    angle. 

A 

416 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  quartz. 

(Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Orthorhombic.  In  thin  tab- 
ular crystals  or  scales. 
Bladed  or  foliated  structure. 

Pearly  luster  on  cleavage  face,  else- 
where vitreous.  Often  associated 
with  corundum,  chlorite,  marga- 
rite,  etc. 

Diaspore. 
AIO(OH). 

Orthorhombic.  In  prismatic 
crystals,  deeply  striated  ver- 
tically and  seldom  distinctly 
terminated.  Also  massive, 
columnar  to  compact. 

Pearly  luster  on  cleavage  face,  else- 
where vitreous. 

Zoisite. 
Ca2(Al.OH)AI2 
(Si04),. 

Orthorhombic.  Commonly 
in  long  slender  unterminated 
crystals.  Often  in  close  par- 
allel groups.  Fibrous,  co- 
lumnar. 

In  schistose  rocks. 

Sillimanite 
(Fibrolite). 
Al2SiO6. 

Monoclinic.  In  slender  pris- 
matic crystals,  striated  par- 
allel to  length  of  crystal. 
Also  fibrous,  granular. 

Characterized  by  its  olive-green 
color.  When  transparent  shows  di- 
chroism;  i.e.,  in  transmitted  light 
ippears  green  in  one  position  and 
brown  in  another.  In  metamorphic 
rocks;  often  in  crystalline  lime- 
stones. 

EPIDOTE. 

CMAl.OH) 
(Al,Fe)2(SiO4)3. 

Bladed. 

See  p.  403. 

CYANITE. 
AljSiOfi. 

Radiating  prismatic. 

See  p.  405. 

NATROLITE. 
Na2Al(AlO) 
(Si03)3.2H20. 

Monoclinic.  In  cleavable 
masses  or  in  irregular  grains 
as  a  rock  constituent.  May 
be  in  crystals,  see  Figs.  269- 
271,  p.  221. 

Orthoclase  is  monoclinic  while  mi- 
crocline  is  triclinic.  Ordinarily 
they  can  only  be  told  apart  by  a 
microscopic  examination.  The 
green  amazon  stone  is  usually  mi- 
crocline.  Characterized  by  its  2 
cleavage  planes  at  righ  angles;  the 
:>asal  cleavage  is  the  better. 
Found  as  a  prominent  constituent 
of  granite  rocks  and  pegmatite 
veins,  associated  with  quartz  and 
mica. 

ORTHOCLASE, 

Microcline 
(Potash  Feldspar). 
KAlSi,0,. 

417 


NONMETALLIC 

II.     Give  a 

4.  Cannot  be  scratched  by  a  knife, 

a.     Show  a  prominent 


Cleavage. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

C.  Basal  per- 
fect. C.  Pina- 
coidal  not  so 
distinct.  The 
two  make  an- 
gles with  each 
other  varying 
from  85°  50'  to 
86°  24'. 

Colorless,     white, 
gray,  greenish, 
bluish,     reddish. 
Often     exhibit     a 
beautiful    play    of 
color  on  the  cleav- 
age surfaces. 

Vitreous,  pearly. 

6 

2.6-2.7 

J     C.     Prismatic. 

1 
.a 

White,  gray,  pink, 
emerald-green 

Vitreous. 

6.5 

3.2 

fi     C.      Prismatic 
g     making    angles 
3     of  5$°  and  125°. 

White  to  green  to 
black. 

Vitreous,  pearly. 

5-6 

3.0-3.3 

C.  Prismatic. 
Perfect  at  an- 
gles of  54°  and 
126°. 

Gray,  clove- 
brown,  green. 

Vitreous,  pearly. 

5.5-6 

3.1 

C.  Prismatic. 
Not  very  per- 
fect at  angles 
nearly  90°. 

Greenish  to  brown- 
ish black. 

Vitreous. 

6-6.5 

3.5 

C.  Prismatic. 
Rather  poor  at 
90°  angles. 

White  to  green  to 
black. 

Vitreous. 

5-6 

3.1-3.5 

418 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  quartz. 

cleavage.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Triclinic.  In  cleavable 
masses  or  in  irregular  grains 
as  a  rock  constituent.  Al- 
bite  may  be  in  thin  tabular 
crystals  or  with  a  curved 
lamellar  structure. 

Albite  =  NaAlSi3O8;  Oligoclase  = 
3NaAlSi308  lCaA!2Si2O8;  Andesine 
=  !NaAlSi3O8  lCaAl2Si2O8;  Lab 
radorite  =  lNaAlSi3O83CaAl2Si2O8 
Anorthite  =  CaAl2Si2O8.  Charac 
terized  b.,  a  perfect  basal  cleavage 
and  a  pinacoidal  cleavage  not  so 
distinct;  the  two  making  an  angle 
with  each  other  of  nearly  90° 
Often  on  the  best  cleavage  surface 
will  be  seen  a  series  of  fine  parallel 
striation  lines  due  to  intimate 
twining.  Often  they  show  a  fine 
play  of  colors  on  cleavage  surfaces, 
>ale  blue  in  albite  and  oligoclase; 
>right  blue,  green,  gold,  etc.,  hi  an- 
desite  and  labradorite.  Rock  con- 
stituents; albite  and  oligoclase  in 
the  light  colored  granitic  rocks;  the 
others  in  the  darker  colored,  more 
>asic  igneous  rocks. 

THE 
PLAGIOCLASE 
FELDSPARS. 

Combinations    in 
varying  amounts  of 
NaAlSi308,  the   Al- 
bite molecule,  and  of 
CaAl2Si2O8,  the  An- 
orthite molecule. 

Monoclinic.  In  flattened 
prismatic  crystals,  vertically 
striated;  sometimes  very 
large.  Also  massive,  cleav- 
able. 

jilac  to  pink  called  kunzite.  Green 
s  called  hiddenite.  Often  alters  to 
other  minerals  with  a  dull  gray 
color.  Not  common. 

SPODUMENE. 
(Li,Na)Al(SiO3)2. 

Monoclinic.  In  slender  pris- 
matic crystals,  showing 
prominent  cleavage. 

See  p.  407. 

AMPHIBOLE 
GROUP. 

Orthorhombic.  Commonly 
lamellar  or  fibrous  massive; 
fibers  often  very  slender. 
Also  in  aggregates  of  prisms. 
Distinct  crystals  rare. 

Characterized  by  its  cleavage  an- 
;le.  Sometimes  fibrous  (asbesti- 
orm.  Not  common.  An  ortho- 
hombic  amphibole. 

Anthophyllite. 
(Mg,Fe)SiO,. 

Monoclinic.  Long  prismatic 
crystals,  vertically  striated. 
Acute  terminations  charac- 
teristic. Also  in  groups  of 
acicular  crystals.  Fibrous. 

A.  rare  mineral. 

Acmite 
(^girite). 
NaFe(SiO,)j. 

Monoclinic.  In  stout  pris- 
matic crystals  with  rectan- 
gular cross-section. 

See  p.  407. 

PYROXENE 
GROUP. 

419 


NONMETALLIC 

II.     Give  a 

4.  Cannot  be  scratched  by  a  knife, 

a.     Show  a  prominent 


Cleavage. 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

|     Enstatite     has 
5     fair     prismatic 
I,    C.,at90°. 
JHypersthene 
has  perfect 
g     pinacoidal  C. 

£ 

Gray-brown, 
green,  bronze- 
brown,  black. 

Pearly,  bronze- 
like. 

5.5-6.5 

3.2-3.3 

&     C.      Prismatic 
£     at  nearly  90°. 

Rose-red,  pink, 
brown. 

Vitreous. 

5-6 

3.6 

C.      Basal  and 
pyramidal. 

Yellow,       brown, 
blue,  black. 

Adamantine. 

5.5-6 

3.8-3.9 

Dodecahedral 
C.,    seldom 
seen. 

White,  gray,  blue, 
green. 

Greasy,  vitreous. 

5.5-6 

2.1-2.3 

b.     Do  not  show  a 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

Colorless  or 
white. 

Vitreous. 

F.     Uneven. 

5-5.5 

2.3 

£-§Gray,  white. 
2  J2  colorless. 

gl 

'J9f*> 

Vitreous  to  dull. 

F.    Uneven. 

5.5-« 

2.5 

*T3 

J*§  Colorless,  pale 
<D  green,  yellow. 

o  1 

Vitreous. 

F.     Uneven. 

5-5.5 

2.9-3.0 

"3  o 
^Colorless. 
S3     white,  to  pale 
•JJ  yellow. 

Vitreous. 

F.     Uneven. 

7 

3.0 

50  White,    gray, 
light  to  dark 
green,  brown. 

Vitreous  to  dull. 

F.    Uneven.    Pris- 
matic C.,  seldom 
seen. 

5-6 

2.7 

420 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  quartz. 

cleavage.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Orthorhombic.  Crystals 
usually  prismatic  but  rare. 
Commonly  massive,  fibrous 
or  lamellar. 

Enstatite  is  light  colored;  with  in- 
crease of  iron,  bronzito,  is  olive- 
green  to  brown,  often  with  bronze- 
like  reflections;  hypersthene,  rich 
in  iron,  is  dark  green  to  almost 
black.  An  orthorhombic  pyroxene. 

ENSTATITE 
(Bronzite). 
MgSiO3. 
Hypersthene. 
(Fe,Mg)Si03. 

Triclinic.  Usually  massive, 
cleavable  to  compact. 

See  p.  407. 

RHODONITE. 
MnSiO3. 

Tetragonal.  In  pyramidal 
crystals.  At  times  tabular 
with  promin  nt  basal  plane. 

A  rare  mineral. 

Octahedrite 
(Anatase). 
TiO2. 

Isometric.  Massive  or  in 
e-n  bedded  grains.  Rarely  in 
dodecahedral  crystals. 

Frequently  blue.  A  rock-making 
mineral,  never  associated  with 
quartz.  Opaque  to  translucent. 

Sodalite. 
Na4(AICl)Al, 

(SiO4)s. 

prominent  cleavage. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

In  trapezohedrons. 

See  p.  411. 

ANALCITE. 

NaAl(SiO,)2H2O. 

Isometric.  In  trapezohe- 
drons. 

Characterized  by  its  crystals. 
Usually  gray  in  color  and  -with  a 
dull  luster.  Translucent  to  opaque. 
Found  as  phenocrysts  in  basic 
igneous  rocks,  never  with  quartz. 

LEUCITE. 
KAl(SiO,)2. 

Monoclinic.  Usually  crys- 
tallized. 

See  p.  411. 

DATOLITE. 
Ca(BOH)SiO4. 

Orthorhombic.  In  prismatic 
crystals. 

See  p.  429. 

Danburite. 
CaB2(Si04),. 

Tetragonal.  Prismatic  crys- 
tals, granular  or  massive. 

Often  altered.  Opaque  to  translu- 
cent. 

SCAPOLITE. 
Ca4AUSijO26  with 
Na4Al,Si,0,4Cl. 

421 


NONMETALLIC 

II.     Give  a 

4.  Cannot  be  scratched  by  a  knife, 

b.     Do  not  show  a 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

Colorless, 
gray,  greenish, 

Greasy,  vitreous. 

F.    Uneven.    Pris- 
matic C.,  seldom 
seen. 

5.5-6 

2.6 

Apple-green, 
gray,  white. 

Vitreous. 

F.     Uneven. 

6-6.5 

2.9 

d. 

S 

•3     Yellow- 

Vitreous. 

F.    Uneven.    May 

5.5 

4-4.1 

jj  3     green,  white, 

show   fairly   good 

«  -^     colorless, 

C. 

*/§     blue,      gray, 

*     brown. 

•5* 

-S3    ' 

o"c3     Olive    to 

Vitreous. 

F.     Uneven.     C., 

6.5-7 

3.3 

^"i     grayish- 

rarely  seen. 

jd  •     green,  brown. 

•jj  ^     Green, 

Vitreous. 

F.     Uneven. 

7-7.5 

3-3.1 

O  a    brown,   blue, 

<u     red,     pink, 
•a     white,  black. 

! 

i 

1     Green, 

Vitreous,  resinous. 

F.    Uneven. 

6.5 

3.4 

_®     brown,    yel- 

M     low,    blue, 

red. 

White   to 
green    to 

Vitreous. 

F.      Uneven. 
Rather  poor  pris- 

5-6 

3.1-3.4 

black. 

matic  C.,   at  90° 

angles. 

Clove-brown,  gray, 

Vitreous. 

F.        Conchoidal. 

6.5-7 

3.3 

green,  yellow. 

Pinacoidal  C.,  not 

prominent. 

422 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  quartz. 

prominent  cleavage.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Hexagonal.  Usually  mas- 
sive. Rarely  in  small  prisms. 

A  rock-making  mineral.  Com- 
monly found  in  igneous  rocks  which 
do  not  contain  quartz.  Usually 
opaque  to  translucent  with  a  greasy 
luster. 

NEPHELITE. 
NaAlSiO4. 

Orthorhombie.  Reniform, 
globular  and  stalactitic  with 
crystalline  surface.  In  groups 
of  tabular  crystals,  often  bar- 
rel-shaped. Distinct  crys- 
tals rare. 

Characterized  by  its  structure  and 
pale  green  color.  Translucent. 

PREHNITE. 
HzCasAlzlSiO,),. 

Massive  and  in  disseminated 
grains.  Rarely  in  hexagonal 
prismatic  crystals. 

Characterized    by    its    color    and 
franular  structure.     Associated  at 
'ranklin  with  red  zincite  and  black 
franklinite.     Troostite  is  brown  or 
gray  in  color. 

WILLEMITE. 

Zn2SiO4 
Troostite. 
(Zn,Mn)2SiO4. 

Orthorhombie.  Usually 
granular  either  in  masses  or 
disseminated. 

Characterized  usually  by  its  green 
color,  glassy  luster  and  granular 
structure.  Occurs  in  basic  igneous 
rocks. 

CHRYSOLITE 

(Olivine,  Peridot). 
(Mg,Fe)2SiO4. 

Hexagonal,  rhombohedral. 
Usually  in  slender  prismatic 
crystals. 

See  p.  431. 

TOURMALINE. 

A  complex  boron  sil- 
icate  containing 
chiefly  Al,  Fe,  Mg, 
Mn,  alkalies,  F  and 
OH. 

Tetragonal.  In  square  pris- 
matic crystals  terminated 
usually  by  base  and  pyramid. 
Often  columnar.  Granular 
massive. 

Usually  green  or  brown  in  color. 
Transparent  to  translucent.  Often 
occurs  in  crystalline  limestones. 

VESUVIANITE 

(Idocrase) 
Ca6(Al(OH,F)) 
(Al,Fe)2(SiO4)6. 

Monoclinic.  In  stout  pris- 
matic crystals  with  rectan- 
gular cross-section. 

See  p  407. 

PYROXENE 
GROUP. 

Triclinic.  Crystals  with 
acute  edges,  wedge-shaped. 
Also  lamellar,  lamellae  often 
curved. 

Characterized  by  its  crystal  habit. 
Transparent  to  translucent.  Not 
common. 

Axinite. 
Ca7Al4B2(Si04)8. 

423 


NONMETALLIC 

II.     Give  a 

Cannot  be  scratched  by  a  knife, 

b.     Do  not  show  a 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

Red-brown  to 
brownish 
black. 

Resinous,  vitreous, 
dull  when  altered. 

F.    Uneven. 

7-7.5 

3.8 

Reddish 
brown,  flesh- 
red,  olive- 
green. 

Vitreous,   dull 
when  altered. 

F.      Uneven.     C. 
seldom  prominent. 

7.5 
Softer     when     al- 
tered. 

3.2 

Brown,      gray, 
green,  yellow. 

Resinous,  adaman- 
tine. 

F.    Uneven.    Pris- 
matic  C.    seldom 
prominent. 

5-5.5 

3.4-3.5 

•°     Yellowish      to 
•g     reddish  brown. 

Resinous. 

F.     Uneven. 

5-5.5 

5.2-5.3 

w     Brown  to 
§     black. 

Adamantine. 

F.     Uneven. 

6-7 

6.8-7.1 

•     Reddish 
>>    brown  to  black. 

y 

Adamantine. 

F.      Uneven.     C. 
not  prominent. 

6-6.5 

4.2 

Hair-brown  to 
black. 

Adamantine. 

F.     Uneven. 

6. 

4.0 

Brown  to  pitch- 
black. 

Pitchy  or  resinous. 

F.    Uneven  to  con- 
choidal. 

5.5-6 

3.5-4.2 

Blue,  rarely 
colorless. 

Vitreous. 

F.   Conchoidal. 
C.    Pinacoidal  not 
prominent. 

7-7.5 

2.6 

424 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  quartz. 

prominent  cleavage.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Orthorhombic.  In  pris- 
matic crystals. 

See  p.  433. 

STAUROLITE. 
(A1O)<(A1.OH) 
Fe(SiO<)2. 

See  p.  431. 

Andalusite 
(Chiastolite). 
Al2SiO6. 

Monoclinic.  Wedge-shaped 
crystals. 

Seep.  411. 

TITANITE 
(Sphene). 
CaTiSiOj. 

Monoclinic.  Granular. 

A  rare  mineral.     Heavy. 

MONAZITE. 
(Ce,  La,  Di)PO4 
often  with  ThSiO4. 

In  irregular  masses;  in  rolled 
grains. 

See  p.  431. 

CASSITERITE. 
(Tin  Stone)  SnO,. 

Tetragonal.  In  prismatic 
crystals  vertically  striated; 
often  slender  acicular.  Crys- 
tals frequently  twinned. 

Usually  gives  a  light  brown  streak. 
Usually  opaque  to  translucent. 

RUTILE. 
TiO2. 

Orthorhombic.  Only  in 
crystals.  Habit  varied;  tab- 
ular; prismatic;  resembling 
hexagonal  pyramids,  etc. 

A  rare  mineral. 

Brookite. 
TiO2. 

Monoclinic.  Massive  and  in 
embedded  grains.  Crystals 
often  tabular. 

A  rare  mineral. 

Allanite. 
R2"(R.OH)R2'" 
(SiO,),. 
R"=Ca  and  Fe. 
R"  =Al,Fe,Ce,La 
Di. 

Orthorhombic.  In  em- 
bedded grains;  also  massive, 
compact.  In  six-sided  pris- 
matic crystals. 

Transparent  to  translucent.     Most 
commonly  found  altered  with  foli- 
ated   structure,    a    grayish    green 
color,  and  softer  than  a  knife. 

lolite 
(Cordierite). 
H2(Mg,Fe)4 
AlsSi10On. 

425 


NONMETALLIC 

II.     Give  a 

4.  Cannot  be  scratched  by  a  knife, 

6.    Do  not  show  a 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

Deep  azure- 
blue,     greenish 
blue. 

Vitreous. 

F.    Uneven. 

5-5.5 

3.0-3  1 

§     Azure-blue. 

5 

Vitreous. 

F.    Uneven. 

5-5.5 

2.4 

Blue,  green, 
white,  gray. 

Greasy,  vitreous. 

F.   Conchoidal. 
Dodecahedral  C. 
seldom  seen. 

5.5-6 

2.1-2.3 

Pink  to  red.    See  tourmaline,  p.  423. 

Black.    The  following  minerals  may  be  almost  or  quite  black;  cassiterite, 

NONMETALLIC 

II.     Give  a 

5.  Cannot  be  scratched 

a.     Show  a 


Cleavage 

Color. 

Luster. 

Hardness. 

Spec. 
Grav. 

Perfect  basal  C. 

Colorless,  yellow, 
pink,  bluish,  green- 
ish. 

Vitreous. 

8 

3.5 

C.    Pinacoidal. 

Hair-brown,  gray, 
grayish  green. 

Vitreous. 

6-7 

3.2 

C.    Prismatic. 

White,  gray,  pink, 
emerald-green. 

Vitreous. 

6.5-7 

3.2 

C.    Octahedral. 

Colorless,  yellow, 
red,  blue,  gray, 
black. 

Adamantine. 

10 

3.5 

See  also  corundum,  p.  429,  which  may  sho'w  a  parting  resembling  cleavage. 

426 


LUSTER. 

colorless  streak. 

but  can  be  scratched  by  quartz. 

prominent  cleavage.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Usually  massive. 

Characterized  by  its  color. 

Lazurite 
(Lapis-  Lazuli). 
(Na2,Ca)2(Al.NaS3) 
Al2(SiO4)3. 

Usually  in  pyramidal  crys- 
tals. 

A  rare  mineral.    Characterized  by 
its  color.    Told  from  lazurite  by  its 
crystals.    Opaque. 

Lazulite. 
(Mg,Fe)(Al.OH)2 
(P04)2. 

Massive. 

See  p.  421. 

SODALITE. 

Na4(AlCl)Al2 
(Si04)3. 

rutile,  brookite,  allanite,  p.  425;  pyroxene  and  tourmaline,  p.  423. 

LUSTER, 
colorless  streak, 
by  quartz. 

prominent  cleavage. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Orthorhombic.  In  prismatic 
crystals,  terminated  by  base, 
pyramids  and  domes.  Also 
coarse  to  fine  granular. 

Characterized  by  its  crystals,  hard- 
ness and  cleavage. 

TOPAZ. 

(AlF)2SiO4 
(OH)  iso.  with  F. 

Orthorhombic.  Commonly 
in  long  slender  crystals. 

See  p.  417. 

Sillimanite 
(Fibrolite). 
Al2SiO6. 

Monoclinic. 

See  p.  419. 

SPODUMENE. 

(Li,Na)Al(SiO,)2. 

Isometric.  In  octahedral 
crystals,  faces  usually  rough 
and  curved.  In  irregular 
rounded  pieces. 

Characterized  by  its  extreme  hard- 
ness.    Hare. 

Diamond. 
C. 

427 


NONMETALLIC 

II.    Give  a 

5.  Cannot  be  scratched 

6.     Do  not  show  a 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

Colorless, 
white, 
smoky,  ame- 
thyst.   Vari- 
ously colored 
when  impure. 

fs 

Vitreous,  greasy. 

F.    Conchoidal 

7 

2.6 

o  u    Colorless, 
gjj'S     white  to  pale 
,»  "S     yellow. 

Is 
»i 

Vitreous. 

F.    Uneven. 

7 

3.0 

«  8    " 

.S32     White,  color- 
Q        less. 

Vitreous. 

F.    Conchoidal. 

7.5-8 

2.9 

White,  gray, 
blue,  yellow, 
brown,  green, 
pink,  red. 

Adamantine    to 
vitreous. 

F.    Uneven. 

9 

4.0 

Lavender, 
blue,     green, 
brown,     red, 
fl.     black. 

Vitreous. 

F.    Conchoidal. 

8 

3.5-3.8 

j^     Bluish  green, 
g     green,  yellow, 
•«     pink,  colorless. 
5 

r 

>> 
i 

Vitreous. 

F.  Conchoidal, 
uneven. 

7-7.5 

2.7 

IB 

0     Yellowish  to 
emerald- 
green. 

Vitreous. 

F.  Conchoidal, 
uneven.        C.  not 
Drominent. 

8.5 

3.6-3.8 

428 


LUSTER. 

colorless  streak, 
by  quartz. 

prominent  cleavage. 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Rhombohedral,  trapezohe- 
dral.  Irregular  massive;  in 
embedded  grains;  as  pebbles, 
sand.  Crystals  usually  show 
hexagonal  prism  terminated 
by  what  appears  to  be  a  hex- 
agonal pyramid.  Prism 
faces  are  striated  horizon- 
tally. Crystals  frequently 
tapering. 

Characterized  by  its  crystals;  its 
conchoidal  fracture  and  vitreous 
luster.  For  description  of  varieties 
see  pp.  175-177.  Transparent  to 
translucent.  Most  common  min- 
eral. 

QUARTZ. 

SiO2. 

Orthorhombic.  In  prismatic 
crystals,  resembling  those  of 
topaz.  Also  disseminated  in 
indistinct  crystals  and  irreg- 
ular masses. 

Characterized  by  its  crystals. 
Distinguished  from  topaz  by  its 
lack  of  cleavage.  Transparent  to 
translucent.  A  rare  mineral. 

Danburite. 
CaB2(Si04)2. 

Rhombohedral.  In  small 
rhombohedral  crystals. 

A  rare  mineral. 

Phenacite. 
Be2SiO4. 

Hexagonal,  rhombohedral. 
In  irregular  masses  showing 
at  times  an  almost  cubic 
structure  owing  to  a  rhombo- 
hedral parting.  In  rude 
prisms,  often  barrel-shaped. 

Characterized  by  its  extreme  hard- 
ness. Ruby  =  red;  sapphire  =  blue; 
various  other  colors.  Emery  is  im- 
pure corundum  usually  with  magne- 
tite. May  show  rhombohedral 
parting  with  nearly  90°  angles. 

CORUNDUM. 

A1203. 

Isometric.  In  octahedrons; 
sometimes  twinned. 

Characterized  by  its  crystals  and 
its  hardness.  Ruby  spinel  when 
red. 

SPINEL. 
MgAl204. 

Hexagonal.  Usually  in  pris- 
matic crystals  with  basal 
plane;  pyramid  faces  rare. 
Sometimes  deeply  furrowed 
vertically.  Crystals  at  times 
large.  Also  irregular,  mas- 
sive. 

Often  shows  a  mottling  of  color  due 
to  alternation  of  transparent  and 
opaque  spots.  Crystals  very  char- 
acteristic. Most  common  color  = 
blue-green,  known  as  aqua-marine; 
also  deep  green  as  emerald;  yellow 
as  golden  beryl;  pink  as  morganite. 
Found  in  pegmatite  veins. 

BERYL. 

Be3Al2(Si03)8iH20. 

>» 

Orthorhombic.  In  tabular 
crystals  which  are  frequently 
twinned  giving  hexagonal 
shapes. 

A  rare  mineral.  Characterized  by 
its  hardness. 

Chrysoberyl 
(Alexandrite). 
BeAl2O4. 

429 


NONMETALLIC 

H.    Give  a 

5.    Cannot  be  scratched 

b.     Do  not  show  a 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

Green, 
brown,   blue, 
M     red,  pink, 
S£     white,  black. 

d. 
^r 

if 

Vitreous. 

F.    Uneven. 

7-7.5 

3.0-3.1 

S-s    " 
aj     Green,  gray, 
•*|     white. 

fS 

5^ 

Vitreous. 

F.    Splintery.    C., 
prismatic    at 
nearly  90°  angles, 
not  prominent. 

7 

3.3 

3§ 
•If  £    Olive  to  gray 
J2     iah  green, 
iB.a     brown, 
•g  aJ 

Vitreous. 

F.      Uneven.      C. 
rarely  seen. 

6.5-7 

3.3 

°1    flreen, 
-^     brown,      yel- 
o    low,  blue, 
o     red. 

Vitreous,  resinous. 

F.     Uneven. 

6.5 

3.4 

J     Dark  green. 

Vitreous. 

F.  Conchoidal, 
uneven. 

7.5-8 

4.5 

Reddish  brown 
•  to  black. 

I       ,  ; 

Adamantine. 

F.     Uneven.      C. 
not  prominent. 

6-7 

6.8-7.1 

•J     Reddish 
O     brown,  flesh- 
red,  olive- 
green. 

Vitreous,  dull 
when  altered. 

F.  Uneven.    C. 
seldom  prominent. 

7.5 

3.2 

430 


LUSTER, 
colorless  streak, 
by  quartz. 

prominent  cleavage.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Rhombohedral.  Usually  in 
slender  prismatic  crystals, 
striated  vertically.  Cross- 
section  usually  resembles  a 
spherical  triangle.  When 
terminated  usually  shows 
base  and  rhombohedrons. 
Often  in  slender  radiating 
crystals. 

Widely  various  in  color.  Most  com- 
monly black.  Of  the  lighter  colors 
jjreen  is  most  frequent.  ^Character- 
:zed  by  its  crystal  *  structure. 
Crystals  exhibit  pyro-electricity; 
i.e.,  after  being  heated  they  will 
attract  and  hold  small  pieces  of  tis- 
sue paper,  etc.,  A  candle  flame  may 
be  used.  Found  in  pegmatite  veins 
and  metamorphic  rocks. 

TOURMALINE. 

A  complex  boron  sil- 
icate  containing 
chiefly  Al.Fe.Mg, 
Mn,  alkalies  F  and 
(OH). 

Always  massive,  usually 
closely  compact. 

Translucent.  A  rare  mineral. 

Jadeite 
(Jade). 
NaAlSi2O». 

Orthorhombic.  Usually 
granular. 

See  p.  423. 

CHRYSOLITE 

(Olivine,  Peridot). 
(Mg,Fe)2SiO4. 

Tetragonal. 

See  p.  423. 

Vesuvianite 
(Idocrase). 
Ca6(Al(OH,F)) 
(Al,Fe)2(Si04)5. 

Isometric.  Usually  in  octa- 
hedrons. Sometimes 
twinned. 

Characterized  by  its.  crystals  and 
hardness.  A  variety  of  spinel;  see 
p.  429. 

Gahnite 
(Zinc  Spinel). 
ZnAl2O4. 

Tetragonal.  In  irregular 
masses;  in  compact  fibrous, 
reniform  structure;  in  rolled 
grains.  Rarely  in  prismatic 
crystals,  twins. 

Very  heavy.  Usually  opaque  to 
translucent.  Often  gives  a  light- 
brown  streak.  Usually  to  be 
scratched  by  quartz  with  difficulty. 
Occurs  as  rolled  grains  in  sand,  in 
pegmatite  veins  and  in  granite 
rocks. 

CASSITERITE 

(Tin  Stone). 
SnO2. 

Orthorhombic.  In  coarse 
prismatic  crystals  with 
nearly  square  cross-section. 

Often  soft  on  surface  due  to  altera- 
tion. Frequently  a  cross-section  of 
a  crystal  will  show  a  dark-colored 
cross  due  to  a  regular  arrangement 
of  impurities  in  the  interior  of  crys- 
tal. Occurs  in  rnetamorphic  rocks, 
usually  clay  slates. 

Andalusite 
(Chiastolite). 
Al2SiOs. 

431 


NONMETALLIC 

II.     Give  a 

5.  Cannot  be  scratched 

6.     Do  not  show  a 


Color. 

Luster. 

Cleavage  and 
Fracture. 

Hardness. 

Spec. 
Grav. 

Clove-brown, 

Vitreous. 

F.   Conchoidal. 

6.5-7 

3.3 

green,  yellow, 

C.    Pinacoidal, 

gray. 

not  prominent. 

Red-brown 
to    brownish 

Resinous,  vitreous. 
Dull  when  altered. 

F.     Uneven. 

7-7.5 

3.7 

d        black. 

jg'3     Brown,    red, 
•o.S     gray,    green, 
jg  £     colorless. 

Adamantine. 

F.   Conchoidal. 
C.  prismatic  not 
prominent. 

7.5 

4.7 

w  > 

sS 

S3  a     Usuallv 

Vitreous. 

F.    Uneven. 

6.5-7.5 

3.1-4.3 

$     brown  to  red. 

jj?02     Also    various 

«        shades  of  yel- 

-S        low,  green, 

u        pink,  etc. 

' 

Yellow  minerals,  see  corundum,  beryl,  p.  429,  axinite  and  garnet  above. 
Pink  to  red  minerals,  see  corundum,  spinel,  boryl,  p.  429,  tourmaline,  p.  431,  and 
garnet  above. 

Black  mineral,  see  tourmaline,  p.  431. 


432 


LUSTER, 
colorless  streak, 
by  quartz. 

prominent  cleavage.     (Continued.) 


Crystallization  and 
Structure. 

Remarks. 

Name  and 
Composition. 

Triclinic. 

See  p.  423. 

Axinite. 
Ca7Al4B2(Si04)9. 

Orthorhombic.  In  prismatic 
crystals;  very  commonly  in 
cruciform  penetration  twins. 

Characterized  by  its  crystals.  May 
ae  altered  to  earthy  material  in 
which  case  it  can  be  softer  than  a 
knife.  Opaque  to  translucent. 
Occurs  in  mica  schist. 

STAUROLITE. 

(AlO)4(Al.OH)Fe 

(SiO4)2. 

Tetragonal.  Usually  in 
small  prisms  terminated  by 
pyramid  of  the  same  order. 
As  rolled  grains  in  sand. 

Characterized  by  its  crystals. 
Usually  opaque. 

ZIRCON. 
ZrSiO4. 

Isometric.  Commonly  as 
dodecahedrons  trapezohe- 
drons  or  a  combination  of  the 
two.  In  rolled  grains. 

Grossularite=Ca3Al2(SiO4)3.  usu- 
ally light  yellow  or  green.     Pyrope 
=  Mg3Al2(Si04)?,  deep  red.       Al- 
mandite  =  Fe3Al2(SiO4)3,  brown  to 
red.    Spes?artite  =  Mn3Al2(SiO4)3) 
red.     Andradite  =  Ca3Fe2(SiO4)3, 
green,    yellow,    brown,    to   black. 
Uvarovite  =  Ca3Cr2(SiO4)3,  emer- 
ald-green.   Characterized  by  crys- 
tal shape  and  commonly  its  red 
color.    An  accessory  rock  mineral. 
Commonly  in  metamorphic  rocks. 
As  sand. 

GARNET. 

R"3R'"2(SiO4)3. 
R"  =  Ca.Mg.Fe.Mn 
R'"  =  Al.Fe.Cr. 

433 


INDEX  TO  DETERMINATIVE  TABLES. 


Acmite,  419 
Actinolite,  407 
Alabandite,  381 
Albite,  419 
Allanite,  425 
Amblygonite,  415 
Amphibole,  407,  419 
Analcite,  411,  421 
Anatase,  421 
Andalusite,  425,  431 
Andesine,  419 
Anglesite,  399 
Anhydrite,  397,  409 
Anorthite,  419 
Anthophyllite,     407, 

419 

Antimony,  375 
Apatite,  413 
Apophyllite,  405 
Aragonite,  411 
Argentite,  373 
Arsenic,  375 
Arsenopyrite,  383 
Atacamite,  391 
Augite,  407 
Axinite,  423,  433 
Azurite,  391 

Barite,  399,  409 
Bauxite,  401,  413 
Beryl,  429 
Biotite,  393 
Bismuth,  381 
Bismuthinite,  375 
Borax,  399 
Bornite,  377 
Bournonite,  375 
Brochantite,  391 
Bronzite,  421 


Brookite,  425 
Brucite,  393 

Calamine,  411 
Calaverite,  377 
Calcite,  397,  407 
Carnallite,  399 
Cassiterite,  389,  425, 

431 

Celestite,  399 
Cerargyrite,  395 
Cerussite,  401 
Chabazite,  409 
Chalcanthite,  391 
Chalcocite,  373 
Chalcopyrite,  377 
Chloanthite,  383 
Chromrte,  379,  385 
Chrysoberyl,  429 
Chrysocolla,  391 
Chrysolite,  423,  431 
Cinnabar,  371,    381, 

387 

Clinochlore,  393 
Cobaltite,  383 
Colemanite,  405 
Columbite,   385 
Copper,  381 
Corundum,  429 
Covellite,  377 
Crocoite,  389 
Cryolite,  401 
Cuprite,  379,  387 
Cyanite,  403,  417 

Danburite,  421,  429 
Datolite,  411,  421 
Diamond,  427 
Diaspore,  417 
434 


Diopside,  407 
Dolomite,  397,  407 

Embolite,  395 
Enargite,  373 
Enstatite,  421 
Epidote,  417 

Fluorite,  409 
Franklinite,  385 

Gahnite,  431 
Galena,  371,  375 
Garnet,  423 
Garnierite,  403 
Genthite,  403 
Gersdorffite,  383 
Goethite,    381,    387, 

389 

Gold,  381 
Graphite,  371 
Greenockite,  401 
Gypsum,  395 

Halite,  397 
Harmotone,  405 
Hematite,   371,   379, 

385,  387 
Heulandite,  405 
Hornblende,  407 
Hypersthene,  421 

Ilmenite,  385 
lolite,  425 

Jadeite,  431 
Jamesonite,  323 

Kaolinite,  401 


INDEX 


435 


Kalinite,  399 

Labradorite,  419 
Lazulite,  427 
Lazurite,  415,  427 
Lepidolite,  397 
Lepidomelane,  393 
Leucite,  421 
Limonite,   371,    381, 

387,  389 
Linnseite,  383 
Lithiophyllite,  403 

Magnetite,  383 
Magnesite,  409 
Malachite,  391 
Manganite,  379 
Marcasite,  383 
Margarite,  397 
Microcline,  417 
Millerite,  377 
Mimetite,  401,  413    / 
Molybdenite,  371 
Monazite,  413,  425 
Muscovite,  393 

Natrolite,    405,    411, 

417 

Nephelite,  423 
Niccolite,  377,  383 
Niter,  395 

Octahedrite,  421 
Oligoclase,  419 
Olivenite,  391 
Olivine,  423,  431 
Orpiment,  391 
Orthoclase,  417 

Pectolite,  405,  411 
Pentlandite,  377 
Phenacite,  429 


Phlogopite,  393 
Platinum,  381 
Plagioclase'Feldspars, 

419 

Polybasite,  373 
Prehnite,  423 
Proustite,  387 
Psilomelane,  373,  385 
Pyrargyrite,  379,  387 
Pyrite,  383 
Pyrolusite,  371,  373 
Pyromorphite,  413 
Pyrophyllite,  393 
Pyrrhotite,  377 
Pyroxene,    407,   413, 

419,  423 

Quartz,  429 

Realgar,  389 
Rhodochrosite,  409 
Rhodonite,  407,  421 
Rutile,  389,  425 

Scapolite,  411,  421 
Scheelite,  413 
Serpentine,  403,  415 
Siderite,  409 
Sillimanite,  417,  427 
Silver,  381 
Smalltite,  383 
Smithsonite,  409,  411 
Sodalite,     409,    415, 

421,  427 
Soda  Niter,  395 
Sphalerite,  379,  389, 

409 

Spinel,  429 
Spodumene,  419,  427 
Stannite,  375 
Staurolite,  425,  433 


Stephanite,  373 
Stibnite,  371,  375 
Stilbite,  403 
Stromeyerite,  373 
Sulphur,  391,  395 
Sylvanite,  377 
Sylvite,  395,  397 

Talc,  393 
Tantalite,  385 
Tellurium,  375 
Tetrahedrite,  373 
Thorite,  389 
Titanite,  411,  425 
Topaz,  427 
Tourmaline,  423,  431 
Tremolite,  407 
Triphyllite,  403 
Turgite,  379,  385, 387 

Uraninite,  385 

Vanadinite,  401 
Vesuvianite,  423,  431 
Vivianite,   391,    395, 
397 

Wavellite,  403,  415 
Willemite,  415,  423 
Witherite,  397,  401, 

405,  411 
Wolframite,  379,  385 

389 

Wollastonite,  405,415 
Wulfenite,  413 

Xenotine,  413 

Zincite,  389 
Zircon,  433 
Zoisite,  417 


APPENDIX  I. 


LIST   OF   MINERALS   SUITABLE    FOR    A    SMALL 
MINERAL  COLLECTION. 

For  the  convenience  of  those  who  desire  to  possess  a  small 
but  representative  mineral  collection  the  following  list  is  given. 
The  names  of  the  more  important  species  are  printed  in  black- 
face type,  and  the  names  of  other  desirable  but  less  important 
minerals  in  ordinary  type.  The  first  list  includes  59  names, 
while  the  complete  list  numbers  109. 


Graphite 

Sulphur 

Gold  in  quartz 

Silver 

Copper 

Orpiment 

Stibnite 

Molybdenite 

Galena 

Argentite 

Chalcocite 

Sphalerite 

Cinnabar 

Millerite 

Niccolite 

Pyrrhotite 

Bornite 

Chalcopyrite 

Pyrite 

Marcasite 

Arsenopyrite 

Tetrahedrite 

Halite 

Fluorite 

Cryolite 

Quartz    (several 

varieties) 
Opal 
Cuprite 
Zincite 
Corundum 
Hematite 
Spinel 
Magnetite 
Franklinite 
Chromite 
Cassiterite 
Rutile 


Pyrolusite 

Manganite 

Limonite 

Brucite 

Calcite 

Dolomite 

Siderite 

Rhodochrosite 

Smithspnite 

Aragonite 

Witherite 

Strontianite 

Cerussite 

Malachite 

Azurite 

Orthoclase 

Albite 

Oligoclase 

Labradorite 

Leucite 

Pyroxenes  (several 
varieties) 

Spodumene 

Pectolite 

Rhodonite 

Amphibole  (sev- 
eral varieties) 

Beryl 

Garnet 

Chrysolite 

Willemite 

Scapolite 

Vesuvianite 

Zircon 

Topaz 

Andalusite 

Cyanite 

Datolite 


Epidote 
Prehnite 

Calamine 

Tourmaline 

Staurolite 

Apophyllite 

Heulandite 

Stilbite 

Chabazite 

Analcite 

Natrolite 

Muscovite 

Lepidolite 

Biotite 

Phlogopite 

Clinochlore 

Serpentine 

Talc 

Kaolinite 

Chrysocolla 

Titanite 

Columbite 

Monazite 

Apatite 

Pyromprphite 

Mimetite 

Vanadinite 

Turquois 

Uraninite 

Barite 

Celestite 

Anglesite 

Anhydrite 

Wolframite 

Scheelite 

Wulfenite 


436 


APPENDIX   II.     MINERAL   STATISTICS. 

INTRODUCTION. 

Brief  statistics  relative  to  the  amount  and  value  of  the  pro- 
duction of  the  different  economic  minerals  and  metals  are  pre- 
sented below.  The  figures  have  been  taken  from  the  bulletin 
of  the  United  States  Geological  Survey  entitled  Mineral  Re- 
sources of  the  United  States  for  1915.  Unless  otherwise  stated 
all  statistics  refer  to  productions  from  the  United  States.  It 
should  be  noted  that  because  of  the  European  war  the  condi- 
tions affecting  mineral  production  during  1915  were  abnormal 
in  several  respects.  In  the  case  of  many  metals  there  was  a 
marked  increase  in  the  amounts  produced  and  the  prices  obtained 
were  exceptionally  high. 

SUMMARY   OF  THE   MINERAL  PRODUCTION 
OF  THE   UNITED   STATES   FOR   1915. 

Metals. 

Pig  Iron $401,409,604      Zinc $113,617,000 

Silver 37,397,300       Mercury 1,826,912 

Gold 101,035,700      Aluminum 17,985,500 

Copper 242,902,000 

Lead 47,660,000              Total $993,000,000 

Nonmetals. 

Bituminous  Coal.  $502,037,688  Sand  (Molding,  etc.)  $21,514,977 

Anthracite  Coal. .  184,653,498      Slate 4,958,915 

Natural  Gas 101,312,381       Stone. 74,595,352 

Petroleum 179,462,890       Borax 1,677,099 

Clay   Products..  163,120,232      Gypsum 6,596,893 

Cement 75,155,102  Phosphate  Rock.  .  .  5,413,449 

Ume 14,336,756       Pyrite 1,674,933 

437 


438  APPENDIX 


Nonmetals  (Continued) 

Sulphur $5,954,236*     Glass  Sand $1,606,640 

Salt 11,747,686      Graphite 429,631 

Mineral  Paints .  .  15,514,059       Mica 428,769 

Asphalt 5,242,073       Mineral  Waters 5,138,794 

Bauxite 1,514,834      Quartz 273,553 

Feldspar. .  . ' 629,356      Talc 1,891,582 

Gems 170,431       Tungsten  Ores 4,100,000 


Total $1,393,565,098 

Total  value  of  all  mineral  products  =  $2,393,831,951. 
*  1914. 

Aluminium. 

The  production  of  bauxite,  the  ore  of  aluminium,  in  1915  had 
a  value  of  $1,514,834.  The  consumption  of  the  metal  totaled 
99,806,000  pounds.  Its  price  varied  from  19  to  60  cents  per 
pound. 

Antimony. 

Only  a  small  amount  of  antimony  ore  is  mined  in  the  United 
States.  The  domestic  source  of  the  metal  is  largely  confined 
to  the  smelting  of  antimonial  lead  ores  where  it  is  obtained  in 
the  nature  of  a  by-product.  The  total  value  of  the  antimony 
produced  during  1915,  was  $2,100,000. 

Apatite,  see  Phosphate  Rock. 

Arsenic. 

Arsenic,  chiefly  in  the  form  of  the  oxide,  is  produced  by  only  a 
few  companies  in  the  United  States  and  the  total  production  is 
comparatively  small.  It  is  practically  all  obtained  as  a  by- 
product from  the  smelting  of  ores  that  contain  small  amounts 
of  the  metal.  A  large  part  of  the  production  comes  from  the 
smelting  of  the  copper  ores  at  Butte,  Montana,  which  contain 
arsenic  in  the  form  of  the  mineral  enargite.  The  amount  of 
arsenic  oxide,  or  white  arsenic,  produced  in  1915  was  5,498  tons 
with  a  value  of  $302,116. 


APPENDIX 


439 


Asbestos. 

The  amount  of  asbestos  produced  is  small,  amounting  to 
$76,952  worth  in  1915.  Imports  for  the  same  year  had  a  value 
of  $1,981,483. 

Barite. 

The  value  of  the  barite  produced  in  1915  was  $381,032.  The 
largest  amount  came  from  Missouri. 

Bauxite,  see  Aluminum. 

Bismuth. 

Little  bismuth  was  produced  in  1915.  Imports  of  the  metal 
reached  the  value  of  $108,288. 

Borax. 

A  considerable  amount  of  the  borates  produced  in  the  United 
States  comes  from  the  mineral  colemanite.  All  the  borates 
mined  are  grouped  together,  however,  under  the  title  borax. 
The  value  of  the  production  for  1915  was  $1,677,099. 

Calcite. 

Following  are  the  .statistics  for  the  production  of  Portland 
Cement  for  1915. 


Quantity  in 
Barrels. 

Value  of 
Shipments. 

Pennsylvania         

28,648,941 

$20,252,961 

Indiana 

8,145,401 

7,336,821 

Kansas 

3,580,287 

2,826,443 

California 

4,503,306 

6,338,918 

Illinois                                                 

5,156,869 

4,884,026 

Missouri                                  

4,626,771 

4,007,679 

New  Jersey                     

1,579,173 

1,473,499 

Michigan 

4,765  294 

4,454,608 

New  York 

5,043,889 

4,039,215 

Iowa   

4,559,630 

4,119,952 

Ohio  

1,948,826 

1,917,920 

Texas                                     

1,939,363 

2,518,233 

Washington                 

1,496,216 

1,790,499 

12  other  states  

9,920,941 

8,795,900 

Total                  

85,914,907 

$74,756,674 

Total  production  of  cement  of  all  classes  for  1915  had  a  value 

of  $74,285,248. 


440 


APPENDIX 


The  value  of  the  production  of  limestone  for  the  year  1915 
follows: 


Illinois $2,864,103 

Indiana 4,204,092 

Missouri 1,927,534 

New  York 3,018,871 

Michigan 1,828,766 


Ohio $4,4051590 

Pennsylvania 6,367,446 

Virginia 1,534,545 

Other  states 9,078,919 

Total ,$35,229,866 


Cement,  see  above. 

Chromite. 

The  production  and  imports  of  chromite  for  the  year  1915 
follow.  Chromite  wholly  from  California,  3,281  tons;  value 
$36,744.  Imported,  chiefly  from  New  Caledonia,  British  South 
Africa,  Portuguese  Africa  and  Canada,  76,455  tons;  value 
$780,061. 

Clay. 

The  total  value  of  the  various  kinds  of  clay  produced  in  1915 
was  $3,971,941.  The  value  of  kaolin  produced  was  $241,520. 
The  value  of  kaolin  imported  during  1915  was  $1,152,778.  The 
total  value  of  all  brick  and  tile  products  was  $125,794,844;  that 
of  pottery  products  was  $37,325,388. 

'  Copper. 

The  amounts  of  copper  produced  in  the  years  1905,  1910  and 
1915  follow: 


1905. 

1910. 

1915. 

Alaska  

Pounds. 

4,900,866 

Pounds. 

4,311,026 

Pounds. 

70,695,286 

Arizona  

235,908,150 

297,250,538 

432,467,690 

California 

16,697,489 

45,760,200 

37  658  444 

Colorado 

9,404,830 

9,307,497 

7  272  178 

Idaho 

7,321,585 

6,877,515 

6  217  728 

Michigan 

230,287,992 

221,462,984 

238,956,410 

Montana 

314,750,582 

283,078,473 

268,263,040 

Nevada       .  . 

413,292 

64,494,640 

67,757,322 

New  Mexico  
Tennessee  . 

5,334,192 

3,784,609 
16,691,777 

62,817,234 
18,205,308 

Utah  

58,153,393 

125,185,455 

175,177,695 

Other  states  

18,735,472 

2,944,795 

2,521,192 

Total  

901,907,843 

1,080,159,509 

1,388,009,527 

APPENDIX 


441 


Note.  —  Practically  the  entire  production  of  Michigan  is 
from  native  copper;  that  of  the  other  states  is  from  various  other 
ores. 

The  value  of  copper  varies  quite  widely  from  year  to  year. 
One  pound  was  worth  about  16.75  c.  in  1900;  15.63  c.  in  1905; 
13  c.  in  1910;  17.47  c.  in  1915. 

The  United  States  furnished  in  1913  approximately  one-half 
of  the  total  world's  production.  Statistics  are  not  available 
for  subsequent  years.  Other  countries  that  have  produced 
notable  amounts  of  copper  are  Mexico,  Spain,  Portugal,  Japan, 
Australasia,  Chile,  Canada,  Germany. 

Corundum. 

The  production  of  corundum  for  abrasive  purposes  is  practi- 
cally negligible.  Since  1898,  when  the  production  was  valued 
at  $275,064,  it  has  rapidly  fallen  until  in  1915  the  only  corundum 
produced  was  in  the  form  of  emery  with  a  total  value  for  the 
year  of  $31,131.  Considerable  amounts  of  emery  are  imported, 
the  value  for  1915  being  $271,649.  The  decline  hi  the  domestic 
production  of  corundum  is  due  in  large  part  to  the  manufacture 
of  the  artificial  abrasives,  carborundum  and  alundum.  The 
value  of  such  materials  produced  in  1915  was  $2,248,778.  For 
the  production  of  corundum  as  sapphire,  see  under  gem  stones. 

Feldspar. 

The  amount  of  feldspar  sold  hi  1915  was  as  follows: 


Quantity. 

Value. 

Connecticut   .         

Tons. 

13,510 

$73,124 

Maine                    

27,878 

191,456 

Maryland  

12,485 

36,861 

New  York 

17,375 

65,988 

Pennsylvania 

15,830 

120,984 

Other  states                   

26,691 

140,943 

Total 

113,769 

$629,356 

442 


APPENDIX 


Fluorite,  Fluorspar. 

The  production  of  fluorite  during  1915  was  as  follows: 
Colorado,  New  Hampshire  and  New  Mexico,  $10,562;  Illinois, 
and  Kentucky,  $753,913. 

Garnet. 

The  value  of  garnet  produced  for  an  abrasive  during  1915  was 
$139,584. 

Gem  Stones. 

The  value  of  the  gems  and  ornamental  stones  produced  in  the 
United  States  for  1915  was  $170,431.  More  than  20  different 
minerals  contributed  to  this  total,  the  majority  of  them  being 
found  in  small  amounts,  however.  The  values  of  the  produc- 
tion of  the  more  important  stones  follow:  Sapphire,  $88,214; 
Tourmaline,  $10,969;  Turquoise  and  turquoise  matrix,  $11,691. 


Gold. 

The  values  of  the  gold  production  in  the  years  1905,  1910  and 
1915  are  given  below. 


1905. 

1910. 

1915. 

Alaska 

$15,630,000 

$16,126,749 

$16  710  000 

Arizona 

2,799,214 

3,149,366 

4,555  900 

California.  .  .             ... 

18,898,545 

19,715,440 

22,547,400 

Colorado  

25,023,973 

20,507,058 

22,530,800 

Idaho   •  

1,075,618 

1,096,842 

1,170,600 

Montana.  ...           .   . 

4,794,083 

3,730,486 

4,978,300 

Nevada  

5  269  819 

18  878  864 

11,883,700 

Oregon.    . 

1  405  235 

679  488 

1  867  100 

South  Dakota  
Utah  

6,989,492 

5,402,257 

7,403,500 
3,907,900 

Other  states  

6,274,102 

5,647,228 

3,483,500 

Total  .  .  . 

$88,159,881 

$94,933  778 

$101,035,700 

APPENDIX 


443 


The  gold  production  of  the  leading  countries  for  the  year  1915 
follows : 

United  States. . . .  $101,035,700      Africa $217,639,599 

Canada 18,936,971       Japan 5,385,917 

Mexico 6,559,275       China 2,804,692 

Russia 28,586,392      India 11,522,457 

Australasia 49,397,797 

Total  including  all  other  countries $470,466,214 


Graphite. 

The  production  of  natural  graphite  hi  1915  was  as  follows: 


Quantity. 

Value. 

Alabama  

Pounds. 
3,474,800 

$204,572 

6  other  states  

5,961,200 

225,059 

Total 

9,436  000 

$429,631 

Artificial  graphite  produced  hi  1915  amounted  to  2,542  tons; 
value,  $99,633. 
Ceylon  produced  graphite  in  1913  with  a  value  of  $2,935,529. 


Gypsum. 

The  value  of  the  gypsum  produced  in  the  various  states  for 
1915  follows: 


California $113,863 

Iowa 1,278,128 


Oklahoma  and  Texas      $814,109 
Utah 75,835 


Kansas 

Michigan 686,309 

New  York 1,267,706 

Ohio 772,520 


250,014      Wyoming 103,110 

Other  states 1,235,299 


Total...: $6,596,893 


444 


APPENDIX 


Iron. 

The  production  in  long  tons  of  the  different  iron  ores  by 
states  is  given  in  the  following  table  for  1915. 


Hematite. 

Limonite. 

Magnetite. 

Alabama  
Michigan                         .  .  . 

4,374,309 
12,514,516 

935,045 

Minnesota 

33  464,660 

New  Jersey                  

415,234 

New  York 

71,207 

927,638 

Pennsylvania 

22,552 

340,757 

Tennessee 

181,509 

100,469 

2,207 

Virginia 

38,506 

309,536 

Wisconsin 

1,095,388 

Other  states 

486,  163 

142,291 

101,048 

Total  

52,227,324 

1,488,709 

1,807,002 

Total  of  all  ores  =  55,526,490  tons. 


Production  of  Lake  Superior  District  by  ranges  in  long  tons. 


Marquette. 

Menominee. 

Gogebic. 

Vermilion. 

Mesabi.* 

1880 

1,384,010 

524,735 

1885 

1,430,862 

690,435 

"  119,590' 

"'227,675' 

1890 

2,863,848 

2,274,192 

2,914,081 

891,910 

1895 

1,982,080 

1,794,970 

2,625,475 

1,027,103 

'  2,839,350' 

1900 

3,945,068 

3,680,738 

3,104,033 

1,675,949 

8,158,450 

1905 

3,772,645 

4,472,630 

3,344,551 

1,578,626 

20,156,566 

1910 

4,631,427 

4,983,729 

4,746,818 

1,390,360 

30,576,409 

1915 

3,817,892 

4,665,465 

4,996,237 

1,541,645 

30,802,409 

Total  to  end  of 

1915 

116,266,083 

98,253,341 

87,900,570 

37,942,442 

369,658,988 

The  Mesabi  District  first  shipped  ore  in  1892. 


Total  for  Lake  Superior  District  to  end  of  1915  =  713,213,051 
tons. 


APPENDIX  445 

Kaolin,  see  Clay. 
Lead. 

The  production  of  lead  in  1915  follows: 

Short  Tons. 

Colorado 32,352 

Idaho 160,680 

Missouri e 195,634 

Utah 106,105 

Other  states 42,241 

Total 537,012 

Its  various  uses  were  divided  in  1909  as  follows: 

Short  Tons. 

White  lead  and  oxides 134,138 

Pipe 52,914 

Sheet 23,421 

Shot 36,433 

Other  purposes 104,094 

The  average  price  of  lead  for  1915  was  4.7  cents  per  pound. 

Limestone,  see  Calcite. 
Magnesite. 

The  production  of  magnesite  for  1915  amounted  to  30,499  tons, 
valued  at  $274,491.  The  imports  of  the  mineral  were  valued  at 
$487,211. 

Manganese. 

The  United  States  produces  only  small  amounts  of  manganese 
ores.  The  output  comes  from  Georgia,  California,  Virginia, 
Arkansas,  etc.,  and  was  valued  in  1915  at  $113,309.  A  larger 
amount  of  manganiferous  ores,  in  which  the  manganese  is  saved 
as  a  by-product,  was  produced.  The  imports  of  manganese 
ores  were  valued  at  $2,655,980. 


446  APPENDIX 

Mercury. 

The  production  of  mercury  (quicksilver)  for  1915  was  as 
follows : 

California,  14,283  flasks  (75  Ibs.  each);  value,  $1,174,881 
Arizona,  Oregon,  Texas,  4,423  flasks  "  442,120 

Nevada,  2,327  "  209,911 

Mica. 

The  total  value  of  the  mica  produced  during  1915  was  $428,769. 
Importations  during  the  same  year  were  valued  at  $692,269. 

Monazite. 

There  has  been  no  domestic  production  of  monazite  since  1910. 
The  importations  of  monazite,  thorium  oxide  and  thorium 
nitrate  for  1915  had  a  value  of  $332,073. 

Nickel. 

No  nickel  ores  are  known  to  have  been  mined  in  the  United 
States  in  recent  years.  The  value  of  the  nickel  ore  and  matte 
imported  during  1915  was  $7,629,686. 

Phosphate  Rock. 

The  production  of  phosphate  rock  during  1915  was  as  follows: 

Value. 

Florida $3,762,239 

Tennessee 1,327,747 

South  Carolina 310,850 

Other  states. 12,613 

Total $5,413,449 

Platinum. 

The  value  of  the  platinum  produced  in  the  United  States  is 
small,  being  $23,500  in  1915.  Russia  produced  200,450  ounces 
in  1905,  275,000  ounces  in  1910,  and  124,000  ounces  in  1915. 
Other  sources  at  present  are  negligible.  The  value  of  importa- 


APPENDIX 


447 


tions  into  the  United  States  of  unmanufactured  and  manu- 
factured platinum  in  1915  amounted  to  more  than  $2,412,008. 
The  price  of  platinum  has  been  steadily  rising.  Platinum  in 
ingots  at  New  York  during  1915  varied  from  $38.00  to  $85.50 
per  ounce. 

Potash  Salts. 

The  value  of  potash  salts  produced  in  the  United  States  in 
1915  was  $342,000.  The  value  of  the  various  salts  imported 
during  1915  was  $3,765,224. 

Pyrite. 

The  production  of  pyrite  by  states  for  1915  follows: 


Long  Tons. 

Value. 

California  

132,270 

$496,111 

Illinois  and  Indiana  
Ohio  

15,821 
10,857 

25,556 
27,404 

Virginia  

145,050 

729,644 

Wisconsin 

13,985 

43,354 

Other  states  . 

76,141 

352,864 

Total....  

394,124 

$1,674,933 

Average  price  per  ton  =  $4.25. 

Quartz. 

Pure  crystalline  quartz,  used  for  pottery,  scouring  soaps, 
paints,  etc.,  brings  about  $2.00  to  $3.50  per  ton  in  its  crude  form. 
The  purer  varieties  of  quartzite  and  sandstone,  used  for  the  same 
purposes,  are  worth  from  $1.00  to  $2.00  a  ton.  The  total  pro- 
duction of  quartz  for  these  purposes,  and  including  that  used  as 
a  flux  or  for  abrading  purposes  for  1915,  had  a  value  of  $273,553. 
The  value  of  the  sandstone  production  in  the  United  States  for 
the  same  year  was  $6,095,800.  Sand,  used  for  glass,  moulding, 
building,  etc.,  was  produced  from  a  great  number  of  states, 
Pennsylvania,  Ohio,  New  York,  Illinois,  New  Jersey,  Indiana 
and  Michigan  leading  in  the  order  named  and  had  a  total  value, 
in  1915,  of  $23,121,617. 


448 


APPENDIX 


Rutile,  see  Titanium. 
Salt. 

The  production  of  salt  in  the  different  important  states  for 
1915  follows: 


Quantity. 

Value. 

California 

(In  barrels  of  280 
Ibs.) 

1  048  457 

$694  070 

Kansas  

3,765,164 

1,035,879 

Michigan 

12  588,788 

4  304  731 

New  York 

11,217,471 

2  976  405 

Ohio 

5,880,243 

1  462  192 

Texas   .  .  . 

444,978 

345,944 

Utah 

394,850 

266,334 

West  Virginia  :  

232,239 

115,143 

Other  states  

2,659,306 

546,988 

Total 

38,231,496 

$11  747  686 

Silver. 

The  amounts  and  values  of  the  silver  production  for  the  years 
1905,  1910  and  1915,  are  given  below: 


19 

05. 

19 

10. 

19 

15. 

Ounces. 

Commer- 
cial Value. 

Ounces. 

Commer- 
cial Value. 

Ounces. 

Commer- 
cial Value. 

Arizona  

2,605,712 

$1,573,850 

2,566,528 

$1,385,925 

5,665,672 

$2,826,500 

Colorado 

11,499,307 

6,945,581 

8,509,598 

4,595,183 

7,199,745 

3,591,900 

Idaho  
Montana  .  ... 
Nevada  
Utah  
Other  states.'. 

8,679,093 
13,231,300 
6,482,081 
11,036,471 
2,738,522 

5,242,172 
7,991,705 
3,915,177 
6,666,028 
1,543,926 

7,369,742 
12,162,857 
12,479,871 
10,466,971 
3,847,942 

3,979,661 
6,567,942 
6,739,130 
5,652,164 
2,183,190 

13,042,466 
14,423,173 
14,453,085 
13,073,471 
7,103,463 

6,506,800 
7,195,600 
7,210,500 
6,522,200 
3,543,800 

Total  

56,272,496 

$33,988,587 

57,598,509 

$31,103,195 

74,961,075 

$37,397,300 

Two  thirds  of  the  world's  total  production  of  silver  comes 
from  Mexico,  United  States  and  Canada,  arranged  in  the  order 
of  their  importance. 


APPENDIX  449 

The  commercial  value  of  silver  varies  quite  widely  from  year 
to  year.  An  ounce  was  valued  in  1900  at  61.6  c.,  in  1905  at 
60.4  c.,  in  1910  at  49.3  c.,  and  in  1915  at  51.9  c. 

Soapstone,  see  Talc. 
Sulphur. 

The  value  of  the  sulphur  produced  in  1914,  chiefly  from 
Louisiana  and  Texas  was  $5,954,236.  The  value  of  the  imports 
for  the  same  year  was  $477,937. 

Talc  and  Soapstone. 

The  production  of  talc  and  soapstone  for  1915  follows. 

New  Jersey  and                                 Vermont $409,652 

Pennsylvania $56,466      Virginia 504,742 

New  York 864,843      Other  states 34,758 

North  Carolina 21,501          Total $1,891,582 

Tin. 

The  domestic  production  of  tin  is  negligible.  The  value  of 
the  imports  of  the  metal  for  1915  was  $38,854,597. 

Titanium. 

Very  little  rutile  is  produced  hi  the  United  States.  The 
localities  in  Nelson  County,  Virginia,  are  the  only  ones  that  have 
been  worked  recently.  The  value  of  the  rutile  produced  from 
them  in  1915  was  $27,500.  The  value  of  the  mineral  varies 
according  to  purity  from  $40  to  $150  per  ton. 

Tourmaline,  see  Gem  Stones. 
Tungsten. 

The  total  value  of  tungsten  concentrates  produced  during 
1915  was  $4,100,000.  These  come  chiefly  from  California  and 
Colorado. 


450  APPENDIX 

Turquoise,  see  Gem  Stones. 
Zinc. 

The  production  of  zinc  in  the  United  States  for  1915  is  given 
below. 

Short  Tons. 

Colorado 52,297 

Kansas 14,365 

Missouri 136,300 

Montana 93,573 

New  Jersey 116,618 

Wisconsin '.  41,403 

Other  states 231,935 

Total 586,491 

The  world's  production  of  spelter  by  countries  for  1913  follows: 

Short  Tons. 

Belgium 217,928 

France  and  Spain 78,289 

Germany 312,075 

Great  Britain 65,197 

United  States 346,676 

Total 1,093,635 


INDEX. 


Note.  —  Names  of  mineral  species  are  printed  in  heavy-faced  type;  synonyms  and 
variety  names  in  italics;  general  matter  in  light-faced  type. 


A. 

Accessory    rock-making    min- 
erals, 343. 

Acicular  structure,  57. 
Acid  potassium  sulphate,  92 
Acmite,  233. 
Actinolite,  237. 
Adamantine  luster,  66. . 
Adularia,  222. 
.ffigirite,  233. 
.ffinigmatite,  240. 
Agalmatolite,  283. 
Agate,  176. 
Alabandite,  144. 
Alabaster,  305. 
Albite,  225. 
Alexandrite,  193. 
Allanite,  259. 
Almandite,  244. 
Altaite,  140. 
Aluminium,  tests  for,  95. 
Aluminium  minerals,  310. 
Amalgam,  131. 
Amazon  stone,  223. 
Amblygonite,  292. 
Amethyst,  176. 
Ammonium  carbonate,  93. 
Ammonium  hydroxide,  93. 
Ammonium  molybdate,  93. 
Ammonium  oxalate,  93. 
Ammonium  sulphocyanite,  93. 
Amorphous  minerals,  363. 
Amphibole,  237. 
Amphibole  Group,  237. 


Analcite,  269. 
Anatase,  196. 
Andalusite,  256. 
Andesine,  228. 
Andesite,  333. 
Andradite,  244. 
Anglesite,  302. 
Anhydrite,  303. 
Ankerite,  209. 
Annabergite,  293. 
Anorthite,  229. 
Anthophyllite,  237. 
Antimony,  124. 
Antimony  minerals,  311. 
Antimony,  tests  for,  95. 
Apatite,  288. 
Apatite  Group,  288. 
Apophyllite,  265. 
Aquamarine,  241. 
Aragonite,  2141 
Aragonite  Group,  213. 
Arfvedsonite,  246. 
Argentite,  138. 
Arkose,  336. 
Arsenic,  123. 
Arsenic  minerals,  312. 
Arsenic,  tests  for,  96. 
Arsenopyrite,  156. 
Asbestos,  279. 
Asterism,  68. 
Atacamite,  172. 
Augite,  231. 
Aurichalcite,  219. 
Aventurine,  176. 
Axinite,  260. 
Azurite,  219. 


451 


452 


INDEX 


B. 

Balas  ruby,  188. 
Banded  structure,  59. 
Barite,  299. 
Barite  Group,  299. 
Barium  chloride,  93. 
Barium  hydroxide,  93. 
Barium  minerals,  313. 
Barium,  tests  for,  96. 
Barytes,  299. 
Basalt,  333. 
Bauxite,  201. 
Bead  tests,  90. 
Beam  balance,  64. 
Beryl,  240. 
Biotite,  275. 
Bismuth,  124. 
Bismuthinite,  136. 
Bismuth  minerals,  313. 
Bismuth,  tests  for,  97. 
Black-band  ore,  211. 
Blackjack,  142. 
Blowpipe,  80. 
Blowpipe  flame,  82. 
Blue  vitriol,  306. 
Bog-iron  ore,  200. 
Boracite,  296. 
Borax,  296. 
Borax,  92. 
Bornite,  148. 
Boron,  tests  for,  97. 
Sort,  117. 

Botryoidal  structure,  58. 
Boulangerite,'  160. 
Bournonite,  160. 
Brachy-axis,  47. 
Brachydome,  48. 
Brachypinacoid,  48. 
Braunite,  193. 
Brazilian  emerald,  264. 
Brittle,  62. 
Brochantite,  304. 
Bromyrite,  170. 
Bronzite,  231. 


Brookite,  196. 
Brown  hematite,  200. 
Brucite,  202. 

C. 

Cadmium  minerals,  313. 
Cairngorm  stone,  176. 
Calamine,  261. 
Calaverite,  158. 
Calcite,  204. 
Calcite  Group,  203. 
Calcium,  tests  for,  98. 
Cancrinite,  243. 
Capillary  pyrites,  146. 
Capillary  structure,  57. 
Carbonado,  117. 
Carbon,  tests  for,  99. 
Carborundum,  184. 
Carbuncle,  247. 
Carnallite,  173. 
Carnelian,  176. 
Cassiterite,  193. 
Cat's  eye,  176,  193. 
Celestite,  301. 
Cerargyrite,  169. 
Cerussite,  217. 
Chabazite,  269. 
Chalcanthite,  306. 
Chalcedony,  176. 
Chalcocite,  141. 
Chalcopyrite,  150. 
Chalcotrichite,  179. 
Chalk,  206,  336. 
Chalybite,  210. 
Chemical  formula,  75. 
Chemical  groups,  74. 
Chessylite,  219. 
Chiastolite,  256. 
Chloanthite,  154. 
Chlorine,  tests  for,  99. 
Chlorite  Group,  277. 
Chlorophane,  171. 
Chlorospinel,  188. 
Chondrodite,  261. 


INDEX 


453 


Chromite,  191. 
Chromium  minerals,  314. 
Chromium,  tests  for,  99. 
Chrysoberyl,  192. 
Chrysocolla,  283. 
Chrysolite,  247. 
Chrysoprase,  176. 
Chrysotile,  279. 
Cinnabar,  144. 
Cinnamon  stone,  245. 
Classification  of  minerals,  114. 
Clay  ironstone,  211. 
Cleavage,  3,  59. 
Clino-axis,  50. 
Clinochlore,  277. 
Clinodome,  52. 
Clinohumite,  261. 
Clinopinacoid,  53. 
Clintonite  Group,  276. 
Closed  tube  test,  87. 
Coatings  on  charcoal,  86. 
Cobalt  bloom,  293. 
Cobaltite,  154. 
Cobalt  minerals,  314. 
Cobalt  nitrate,  93, 
Cobalt,  tests  for,  99. 
Cogwheel  ore,  160. 
Colemanite,  296. 
Coloradorite,  144. 
Color  of  minerals,  67. 
Columbite,  284. 
Columnar  structure,  58. 
Compact  structure,  58. 
Concentric  structure,  58. 
Conchoidal  fracture,  60. 
Conglomerate,  335. 
Constancy  of  interfacial  angles,  5. 
Contact  metamorphic   minerals, 

347. 

Copper,  130. 
Copper  glance,  141. 
Copper  minerals,  314. 
Copper  nickel,  147. 
Copper  pyrites,  150. 
Copper,  tests  for,  99. 


Cordierite,  242. 
Corundum,  181. 
Covellite,  145. 
Crocidolite,  240. 
Crocoite,  303. 
Cryolite,  172. 
Crystal  combinations,  13. 
Crystal,  defined,  1. 
Crystal  distortion,  14. 
Crystal  form,  12. 
Crystal  habit,  13. 
Crystallized  structure,  57. 
Crystallographic  axes,  9. 
Cube,  18. 
Cuprite,  179. 
Cyanite,  257. 
Cymophane,  193. 

D. 

Dacite,  333. 

Danburite,  254. 

Datolite,  257. 

Deltoid  dodecahedron,  29. 

Demantoid,  247. 

Dendritic  structure,  57. 

Desmine,  268. 

Determinative  Mineralogy,  364. 

Determinative  Tables,  369. 

Diamond,  116. 

Diaspore,  198. 

Dimorphism,  80. 

Diopside,  231. 

Dioptase,  250. 

Diorite,  332. 

Diploid,  25. 

Divergent  structure,  57. 

Dodecahedron,  19. 

Dolerite,  332. 

Dolomite,  208. 

Double  refraction,  71. 

Drusy  structure,  57. 

Dry-bone  ore,  212. 

Dry  reagents,  92. 

Dunite,  332. 


454 


INDEX 


E. 

Earthy  structure,  58. 
Elceolite,  242. 
Elastic,  62. 
Electric  calamine,  262. 
Electrum,  125. 
Elements,  115. 
Elements,  list  of,  94. 
Embolite,  169. 
Emerald,  241. 
Emery,  182. 
Enargite,  165. 
Endlichite,  291. 
Enstatite,  231. 
Epidote,  259. 
Erubescite,  149. 
Erythrite,  293. 
Essonite,  245. 
Eucryptite,  234. 

F. 

Fahlore,  162. 
Famatinite,  165. 
Fayalite,  248. 
Feather  ore,  159. 
Feldspar  Group,  220. 
Felsite,  333. 
Fergusonite,  286. 
Fibrolite,  256. 
Fibrous  fracture,  60. 
Fibrous  structure,  58. 
Filiform  structure,  57. 
Flame  tests,  88. 
Flexible,  62. 
Flint,  177. 
Flos  ferri,  215. 
Fluorine,  tests  for,  100. 
Fluorite,  170. 
Fluor  spar,  170. 
Foliated  structure,  58. 
Fosterite,  248. 
Fracture,  60. 
Franklinite,  191. 
Fusion,  83. 


G. 

Gabbro,  332. 
Gadolinite,  258. 
Gahnite,  189. 
Galena,  139. 
Galenite,  139. 
Gangue  minerals,  351, 
Garnet,  244. 
Garnierite,  280. 
Gay  Lussite,  219. 
Genthi^e,  280. 
Geocronite,  160. 
Geode,  59. 
Gersdorffite,  154. 
Geyserite,  178. 
Gibbsite,  203. 
Glauberite,  298. 
Glaucophane,  239. 
Globular  structure,  58. 
Gmelinite,  269. 
Gneiss,  337. 
Goethite,  199. 
Gold,  125. 
Golden  beryl,  241. 
Gold  minerals,  317. 
Gold,  tests  for,  101. 
Goniometers,  6. 
Gossan,  153. 
Granite,  331. 
Granular  structure,  58. 
Graphite,  120. 
Gray  copper,  162. 
Graywacke,  336. 
Greasy  luster,  66. 
Greenockite,  146. 
Grossularite,  244. 
Groundmass,  334. 
Gypsum,  304. 


H. 

Hackly  fracture,  60. 

Halite,  166. 

Hardness  of  minerals,  60. 


INDEX 


455 


Harmotone,  267. 
Hausmannite,  193. 
Haiiynite,  243. 

Heavy  spar,  299. 
Hedenbergite,  231. 
Hematite,  184. 
Hemimorphite,  262. 
Hessite,  140. 
Heulandite,  267. 
Hexahedron,  18. 
Hexagonal  axes,  37. 
Hexagonal  minerals,  357. 
Hexagonal  prisms,  38. 
Hexagonal  pyramids,  39,  40. 
Hexagonal  symmetry,  38. 
Hexagonal  system,  37. 
Hexakistetrahedron,  29. 
Hexoctahedron,  23. 
Hiddenite,  234. 
Hornblende,  237. 
Hornblendite,  332. 
Horn  silver,  169. 
Horseflesh  ore,  149. 
Hiibnerite,  307. 
Humite,  261. 
Hyacinth,  254. 
Hyalite,  178. 
Hyalophane,  223. 
Hydrargillite,  203. 
Hydrochloric  acid,  93. 
Hydrogen  sodium  phosphate,  93. 
Hydrohemalite,  198. 
Hydromagnesite,  220. 
Hydrozincite,  220. 
Hypersthene,  231. 

I. 

Ice,  181. 

Iceland  spar,  206. 

Igneous  rocks,  329. 

Ilmenite,  186. 

Ilvaite,  261. 

Index  of  refraction,  69. 

Indices,  12. 


Indicolite,  264. 
Infusorial  earth, 
lodyrite,  170. 
lolite,  242. 
Iridescence,  68. 
Iridium,  133. 
Iridosmine,  133. 
Iron,  133. 
Iron  minerals,  318. 
Iron  pyrites,  151. 
Iron,  tests  for,  101. 
Irregular  fracture,  60. 
Isometric  angles,  30. 
Isometric  axes,  16. 
Isometric  minerals,  355. 
Isometric  symmetry,  17. 
Isometric  system,  16. 
Isomorphism,  77. 
Isomorphous  groups,  79. 

J. 

Jacinth,  254. 
Jadeite,  234. 
Jamesonite,  159. 
Jargon,  254. 
Jasper,  177. 
Jeffersonite,  231. 
Jolly  balance,  64. 

K. 

Kainite,  168. 
Kalinite,  306. 
Kaolin,  281. 
Kaolinite,  281. 
Kidney  ore,  185. 
Krennerite,  159. 
Kunzite,  234. 

L. 

Labradorite,  228. 
Lamellar  structure,  58- 
Lapis-lazuli,  243. 
Laumontite,  268. 


456 


INDEX 


Lazulite,  293. 
Lazurite,  243. 
Lead,  131. 
Lead  minerals,  319. 
Lead,  tests  for,  102. 
Lepidolite,  274. 
Lepidomelane,  276. 
Leucite,  229. 
Lievrite,  261. 
Limestone,  206,  336. 
Limonite,  200. 
Linnseite,  149. 
Lithiophilite,  287. 
Lithium,  test  for,  103. 
Litmus  paper,  92. 
Lodestone,  189. 
Luster,  65. 

M. 

Macro-axis,  47. 
Macrodome,  48. 
Macropinacoid,  48. 
Magnesite,  209. 
Magnesium,  tests  for,  103. 
Magnetic  pyrites,  147. 
Magnetite,  189. 
Malachite,  218. 
Malleable,  62. 
Mammillary  structure,  58. 
Manganese  minerals,  320. 
Manganese,  tests  for,  104. 
Manganite,  199. 
Manganotantalite,  285. 
Marble,  206,  339.. 
Marcasite,  155. 
Margarite,  277. 
Marialite,  250,  251. 
Marl,  337. 

Massive  minerals,  363. 
Massive  structure,  59. 
Meionite,  250,  251. 
Melaconite,  181. 
'Melanile,  246. 
Menaccanite,  186. 


Meneghinite,  160. 
Mercury,  131. 
Mercury  minerals,  321. 
Mercury,  tests  for,  104. 
Metacinnabarite,  144. 
Metallic  luster,  66. 
Metamorphic  rocks,  337. 
Mica  Group,  271. 
Mica-schist,  338. 
Micaceous  structure,  58. 
Microcline,  223. 
Microcosmic  salt,  92. 
Microlite,  286. 
Milky  quartz,  176. 
Millerite,  146. 
Mimetite,  291. 
Mispickel,  156. 
Mizzonite,  250,  251. 
Molybdenite,  137. 
Molybdenum  minerals,  322. 
Molybdenum,  tests  for,  104. 
Monazite,  286. 
Monoclinic  axes,  50. 
Monoclinic  minerals,  360. 
Monoclinic  prism,  52. 
Monoclinic  pyramid,  51. 
Monoclinic  symmetry,  51. 
Monoclinic  system,  50. 
Monticellite,  248. 
Moonstone,  222,  226. 
Morganite,  241. 
Muriatic  acid,  93. 
Muscovite,  272. 

N. 

Nagyagite,  159. 
Natrolite,  270. 
Nephelite,  242. 
Niccolite,  147. 
Nickel  bloom,  293. 
Nickel  minerals,  322. 
Nickel,  tests  for,  104. 
Niobium,  tests  for,  105. 
Niter,  295. 


INDEX 


457 


Nitric  acid,  93. 
Nonmetallic  luster,  66. 
Noselite,  243. 

O. 

Obsidian,  333. 
Octahedrite,  196. 
Octahedron,  18. 
Oligoclase,  227. 
Olivenite,  293. 
Olivine,  247. 
Onofrite,  144. 
Onyx,  177. 
Oolite,  336. 
Opal,  178. 
Opalescence,  68. 
Open  tube  test,  86. 
Orpiment,  134. 
Ortho-axis,  50. 
Orthoclase,  221. 
Orthodome,  52. 
Orthopinacoid,  53. 
Orthorhombic  axes,  46. 
Orthorhombic  minerals,  359. 
Orthorhombic  prism,  47. 
Orthorhombic  pyramid,  47. 
Orthorhombic  symmetry,  46. 
Orthorhombic  system,  47. 
Oxidizing  flame,  84. 
Oxygen,  tests  for,  105. 

P. 

Palladium,  133. 

Parameters,  10. 

Parting,  59. 

Peacock  ore,  149. 

Pearl  spar,  209. 

Pearly  luster,  66. 

Pectolite,  235. 

Pegmatite  dike,  345. 

Penninite,  277. 

Pentagonal  dodecahedron,  25. 

Pentlandite,  144. 


Percentage  composition,  76. 
Peridot,  247. 
Peridotite,  332. 
Perlite,  333. 
Perovskite,  284. 
Petalite,  220. 
Petzite,  140. 
Phenacite,  249. 
Phenocryst,  334. 
Phillipsite,  267. 
Phlogopite,  275. 
Phonolite,  333. 
Phosgenite,  218. 
Phosphorescence,  68. 
Phosphorite,  289. 
Phosphorus,  tests  for,  106. 
Picotite,  188. 
Pitch  blende,  297. 
Pitchstone,  333. 
Plagioclase  feldspars,  224. 
Plagionite,  160. 
Platinum,  131. 
Platinum  minerals,  323. 
Platinum,  tests  for,  106. 
Play  of  colors,  68. 
Pleonaste,  188. 
Plumose  structure,  58. 
Plutonic  rocks,  330,  331. 
Pneumatolytic  minerals,  348. 
Polarized  light,  72. 
Polianite,  198. 
Pollucite,  230. 
Polybasite,  164. 
Polyhalite,  168. 
Porphyry,  334. 
Potash  alum,  306. 
Potash  feldspar,  221. 
Potassium   iodide   and   sulphur 

mixture,  92. 

Potassium  ferricyanide,  93. 
Potassium  ferrocyanide,  93. 
Potassium,  tests  for,  106. 
Prehnite,  260. 
Primary  vein  minerals,  352. 
Proustite,  161. 


458 


INDEX 


Pseudomorphs,  15. 
Psilomelane,  203. 
Pumice,  333. 
Purple  copper  ore,  148. 
Pyrargyrite,  161. 
Pyrite,  151. 
Pyritohedral  class,  24. 
Pyritohedron,  25. 
Pyrochlore,  286. 
Pyroelectricity,  72. 
Pyrolusite,  196. 
Pyromorphite,  290. 
Pyrope,  244. 
Pyrophyllite,  282. 
Pyroxene,  231. 
Pyroxene  Group,  230. 
Pyroxenite,  332. 
Pyrrhotite,  147. 

Q. 

Quartz,  174. 
Quartzite,  338. 
Quicksilver,  see  Mercury. 

R. 

Radiated  structure,  57. 
Realgar,  134. 
Red  copper  ore,  179. 
Reducing  flame,  84. 
Refraction  of  light,  68. 
Reniform  structure,  58. 
Replacement  deposits,  351. 
Resinous  luster,  66. 
Reticulated  structure,  57. 
Rhodochrosite,  211. 
Rhodolite,  246. 
Rhodonite,  236. 
Rhombohedral  class,  41. 
Rhombohedral  minerals,  358. 
Rhombohedron,  42. 
Rhyolite,  333. 
Riebeckite,  239. 
Rock  crystal,  175. 


Rock-making  minerals,  339. 
Rock  salt,  166. 
Rose  beryl,  241. 
Rose  quartz,  176. 
Rubellite,  264. 
Rubicelle,  188.     .'._ 
Ruby,  182. 
Ruby  copper,  179. 
Ruby  silvers,  161. 
Rutile,  195. 

S. 

SdU,  166. 

Salt  of  phosphorus,  92. 
Samarskite,  286. 
Sandstone,  335. 
Sanidine,  222. 
Sapphire,  182. 
Satin  spar,  305. 
Scalenohedron,  42. 
Scale  of  fusibility,  84. 
Scale  of  hardness,  61. 
Scapolite  Group,  250. 
Schoelite,  308. 
Schefferite,  231. 
Schist,  338. 
Scolecite,  271. 
Scorodite,  293. 
Secondary  enrichment,  352. 
Secondary  vein  minerals,  352. 
Sectile,  62. 

Sedimentary  rocks,  334. 
Selenite,  304. 
Serpentine,  278. 
Shale,  336. 
Siderite,  210. 
Silicon,  tests  for,  107. 
Silky  luster,  66. 
Sillimanite,  256. 
Silver,  129. 
Silver  glance,  138. 
Silver  minerals,  324. 
Silver  nitrate,  93. 
Silver,  tests  for,  108. 


INDEX 


459 


Slate,  338. 
Smaltite,  154. 
Smithsonite,  212. 
Smoky  quartz,  176. 
Soapstone,  280. 
Soda-feldspar,  225. 
Sodalite,  243. 
Soda  niter,  295. 
Sodium  carbonate,  92. 
Sodium,  tests  for,  109. 
Spathic  iron,  210. 
Specific  gravity,  62. 
Specular  hematite,  185. 
Sperrylite,  154. 
Spessartite,  244. 
Sphalerite,  142. 
Sphene,  283. 
Sphenoid,  35. 
Sphenoidal  class,  35. 
Spinel,  187. 
Spinel  Group,  187. 
Spodumene,  233. 
Stalactitic  structure,  58. 
Stannite,  151. 
Staurolite,  264. 
Steatite,  280. 
Stellated  structure,  58. 
Stephanite,  163. 
Stibnite,  135. 
Stilbite,  268. 
Stromeyerite,  142. 
Strontianite,  216. 
Strontium,  tests  for,  109. 
Structure  of  minerals,  57. 
Sublimates  in  closed  tube,  88. 
Sublimates  in  open  tube,  87. 
Sublimates  on  charcoal,  86. 
Submetallic  luster,  67. 
Sulphides,  133. 
Sulphur,  122. 
Sulphuric  acid,  93. 
Sulphur,  tests  for,  109. 
Syenite,  331. 
Sylvanite,  157. 
Sylvite,  168. 


Symmetry,  7. 
Symmetry  axis,  7. 
Symmetry  center,  8. 
Symmetry  plane,  7. 

T. 

Tabular  structure,  58. 
Talc,  280. 
Tantalite,  284. 
Tarnish,  68. 
Tellurium,  123. 
Tellurium,  tests  for,  110. 
Tenacity  of  minerals^  62. 
Tennantite,  162. 
Tenorite,  181. 
Tephroite,  248. 
Test  papers,  92. 
Tetragonal  axes,  31. 
Tetragonal  combinations,  34. 
Tetragonal  minerals,  356. 
Tetragonal  prisms,  32. 
Tetragonal  pyramids,  32,  33. 
Tetragonal  system,  31. 
Tetragonal  symmetry,  31. 
Tetragonal  trisoctahedron,  20 
Tetrahedral  class,  27. 
Tetrahedrite,  162. 
Tetrahedron,  28. 
Tetrahexahedron,  19. 
Thomsonite,  271. 
Thorite,  254. 
Thulite,  258. 
Tiemannite,  144. 
Tiger's  eye,  176. 
Tin  minerals,  325. 
Tin  stone,  193. 
Tin,  tests  for,  111. 
Titanic  iron'  ore,  186. 
Titanite,  283. 
Titanium  minerals,  326. 
Titanium,  tests  for,  111, 
Topaz,  254. 
Tourmaline,  262. 
Trachyte,  333. 


460 


INDEX 


Trapezohedral  class,  45. 
Trapezohedron,  20. 
Travertine,  206,  336. 
Tremolite,  237. 
Triclinic  axes,  54. 
Triclinic  domes,  55. 
Triclinic  minerals,  363. 
Triclinic  pinacoids,  56. 
Triclinic  prisms,  55. 
Triclinic  pyramids,  55. 
Triclinic  symmetry,  55. 
Triclinic  system,  54. 
Trigonal  trisoctahedron,  22. 
Trimorphism,  80. 
Triphylite,  287. 
Tripolite,  178. 
Tri-rhombohedral  class,  45. 
Trisoctahedron,  22. 
Tristetrahedron,  29. 
Trona,  220. 
Troostite,  249. 
Tungsten  minerals,  326. 
Tungsten,  tests  for,  111. 
Turgite,  198. 
Turmeric  paper,  92. 
Turquois,  294. 
Twin  crystals,  15. 

U. 

Uneven  fracture,  60. 
Uralian  emeralds,  247. 
Uraninite,  297. 
Uranium,  tests  for,  112. 
Uvarovite,  244. 

V. 

Vanadinite,  291. 
Vanadium  minerals,  327. 
Vanadium,  tests  for,  112. 
Variegated  copper  ore,  149. 


Veins  and  vein  minerals,  349, 
Verd  antique  marble,  279. 
Vesuvianite,  251. 
Vitreous  luster,  66. 
Vitrophyre,  333. 
Vivianite,  293. 
Volcanic  rocks,  330,  332. 

W. 

Warrenite,  160. 
Water,  tests  for,  101- 
Wavellite,  294. 
Wernerite,  250. 
Wet  reagents,  92. 
White  iron  pyrites,  155. 
Willemite,  249. 
Witherite,  215. 
Wolframite,  307. 
Wollastonite,  235. 
Wulfenite,  308. 
Wurtzite,  148. 

X. 
Xenotime,  286. 

Y. 

Yellow  copper  ore,  150. 

Z. 

Zeolites,  267. 
Zinc  blende,  142. 
Zincite,  180. 
Zinc  minerals,  327. 
Zinc,  tests  for,  112. 
Zinkenite,  160. 
Zircon,  252. 
Zoisite,  258. 


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